Minnesota Twins Physics Day 2021
This Teacher’s Guide is meant to give suggestions and resources to teachers concerning baseball and physics and Student activities.. This packet is divided into student activities, and an APPENDIX that contains teacher resources and suggestion and or information related to the student activities.
At School/Home Activities
*1) Fastball Reaction Time
*2) Reaction Time Using a Baseball Bat
*3) Minimizing Handle Forces
*4) Finding the “Sweet Spot” of a Baseball Bat
*5) Center of Percussion - Determining the Sweet Spot of a Bat
*6) Center of Restitution – Baseball vs Turf
During A Game Activities
The following activities can be modified/adjusted depending on where or how you are watching a baseball game.
1) Catcher’s Strongest Arm
2) Hustle Award
3) How Far Away is the Batter?
4) Whew! That Ball Seemed to Go Quite Fast! How Fast Did the Ball Go?
5) How fast is the runner?
6) Work & Power
7) Pitch Speed
8) Scavenger Hunt / Trivia
Appendix: 1) Term abbreviations, conversions, relationships, constants, etc. 2) Teacher Activity notes 3) Teacher Resources
Station One* Activity One Fastball Reaction Time An exhibit at the Exploratorium http://www.exploratorium.edu/baseball/reactiontime.html
Objective: Estimate reaction time using a computer with an internet access.
Click on the "play ball" button, and then move your cursor over the part of the screen that shows the baseball field. As soon as you see "swing batter," click on your screen as fast as you can.
Fastball Reaction Time imitates a 90-mph fastball thrown by a major league pitcher. While this exhibit doesn't test if you could actually hit a fastball, it does test whether you could react in time to hit one. When you see the "swing batter" screen, a signal in your eye sends a message to a part of your brain that controls your muscles. Your brain must then send a signal to your muscles, telling them to click. Although it takes some time for the signal to travel along each nerve, the major delay in your reaction time occurs at the junction points in between the different nerves involved, and between the nerves and the muscles in your fingers.
Trial Number Reaction Time (s) Average Reaction Time 1 2 3
Station One* Activity Two Reaction Time Using a Baseball Bat
Objective: Each student will be able to obtain his/her reaction time by making simple measurements using a baseball bat
Materials needed: Each group of two will need one baseball bat to find their reaction time.
Suggested Strategy:
The time that it takes you to react to a particular situation is called your reaction time. Your reaction time depends on many factors including the stimulus and the particular part of the body that is to react, i.e., it takes longer to move your foot from the gas to the brake pedal than it does for your fingers to grab something simply because your leg is heavier and it has to move farther.
Today we will be finding the time required for you to grab a dropped object, namely a baseball bat. Brace your hand on the edge of a desk so that the fingers are over the edge ready to grab the bat as it is dropped. Have your partner hold the bat such that its zero centimeter mark is even with the center of your fingers and, at some random time, drop it. Record the distance that the bat fell (where you caught it), during the time that your body was reacting. Do this at least 10 times. It is important that the bat is held even with your fingers (not above or below them) and that it is dropped (not thrown down). ALL readings MUST be recorded but any readings that are way out of line can be crossed out and ignored. (In general, your measurements should be between 10cm and 30cm.) Average your readings and then determine your reaction time. Record your results in the table below:
Trial # Your reaction Your reaction time Your reaction time distance (cm) (based on chart) s (based on equation) s
The reaction time can be determined in several ways. You can use the standard equation for freely falling bodies df =1/2at2+vot+do. Where df is the average distance that the bat fell, a is the acceleration of gravity (980 cm/sec2), t is the time that it takes the bat to fall (the reaction time), vo is the initial velocity (zero) and do is the initial distance (zero). Substituting in yields
t= (2df /a)1/2
An alternate method would be to use the chart of distance and time which is in the Appendix to look up the time corresponding to the average distance that the bat fell.
Station Two* Activity Three:
A baseball bat has three "sweet spots"; one of them is called its "center of percussion" (CP). That's physicist talk for the point where the ball's impact causes the smallest shock to your hands. If you hit a baseball closer to the bat's handle than to the center of percussion, you'll feel a slight force pushing the handle back into the palm of your top hand. If you hit the ball farther out than the CP, you'll feel a slight push on your fingers in the opposite direction, trying to open up your grip. But if you hit the ball right on the CP, you won't feel any force on the handle. To find the CP on a bat, try this simple activity.
A bat A ball A friend
When you hold a bat with your hands at the bottom of the handle (a normal grip), the CP is located about six to eight inches from the fat end of the bat. If you choke up on the bat, the CP moves closer to the fat end. That's because the location of your top hand is the place you want the bat to pivot. Changing your hand's position on the bat changes where that pivot point is, which therefore changes the position of the CP to one that corresponds to the new pivot point. *To find the CP on a bat, hold it parallel to the ground in your hand. Make sure you hold it at the same place you normally do when playing a game. It's easier to feel the push if you hold the bat with only one hand; a two-handed grip helps to counteract the push in either direction. But be sure to hold it with the top hand in its "normal" position, no closer to the handle knob than you normally put your top hand. *Close your eyes, so you can concentrate on the sensations you feel with your hand. Have a friend throw a ball at the bat from a few inches away, starting at the end farthest from your hand and moving down the bat. The harder he or she can throw it, the better (as long as they're able to control where on the bat they're throwing the ball).
hold bat here with one hand
Have your partner throw the ball so it hits the bat in the indicated places IN THE ORDER STATED
Notice how the bat feels in your hand as the ball hits it. When this was tried at the Exploratorium, both a vibration and a force pushing on our hands could be felt. The amount of vibration and "push" varied, depending on where on the bat the ball hit. It might be hard hard to distinguish between the two feelings, but the CP is where you feel the smallest push on the hand.
A bat is essentially a long stick. When you hit a stick off center, two things happen: The entire stick wants to move straight backward, and it also wants to rotate around its center. It's this tendency to rotate that makes the bat's handle push back on or pull out of your hands.
When the ball hits the bat's CP, you don't feel a push or pull as the bat tries to spin. That's because when the bat spins, it pivots around one stationary point. When you hit a ball at the CP, the stationary point coincides with where your top hand is. So your hand feels no push one way or the other. This is important if you want to hit the ball a long way. Every time you hit a ball at a point that's not the CP of your bat, some of the energy of your swing goes into moving the bat in your hands, not to pushing the ball so that it moves away from your farther and faster. If less of the bat's energy goes to your hands, more of it can be given to the ball.
Taken from the Exploratorium
Station Two* Activity Four: Finding the “Sweet Spot” of a Baseball Bat
Purpose: One can determine one of the “sweet spots” or the CP on a baseball bat using a wooden bat and hammer
Materials A bat, hammer, friend (optional)
Procedure and Analysis: Hold the bat, hanging down, loosely between your thumb and index finger, just below the knob on the bat’s handle. Have a friend tap the bat gently with a hammer, starting at the fat end and moving toward the handle. It is easier to do with a friend but this can be done by one person. One should feel a vibration in your fingers whenever the bat is struck, except when the “node” or “sweet spot” is hit; then one feels nothing. You may also hear a slightly different sound when the node is hit.
Explanation: When a bat hits a ball just right, one of the three “sweet spots” of the bat has been hit. One of the sweet spots relates to vibration. An object vibrates in response to being struck. These vibrations travel in waves up and down the length of the object. The vibrations cancel each other at the node. A ball that hits the node will cancel the impact waves, and one will not feel the shaking or stinging of the bat in one’s hand. More energy can go to the ball since little energy is lost to vibrations. The node and center of percussion sweet spots differ from each other. One does not feel any force pushing against the hand when a ball hits the center of percussion.
To learn more about what is going on go to www.exploratorium.edu/baeball/sweetspot.html
This activity has been adapted from an activity at the Exploratorium
Identify the location of the “node” and the “center of percussion”
Station Three* Activity Five Center of Percussion: Determining the Sweet Spot of a Bat
Purpose: Determine one of the “sweet spots” of a baseball bat: the center of Percussion (CP) using a bat as a pendulum.
Materials: Stopwatch, meterstick, 25 cm heavy gauge solid copper wire, ring stand, masking tape, transparency marker, bat.
Background: A physical pendulum is a solid object that oscillates about a fixed pivot point. The pivot point is also called the Center of Oscillation. If the pendulum is pulled back a small amount and released, the pendulum will swing back and forth with a definite time period, T. A simple pendulum (a point mass attached to a string of negligible mass) that has the same period of oscillation has the same length as the distance from the pivot point to the “sweet spot.” The “sweet spot” is also called the Center of Percussion (CP).
The CP is the point on the physical pendulum where a collision with another object will transfer maximum momentum and kinetic energy to the other object. A minimum of energy in the form of vibration will travel along the physical pendulum. There will be a minimum of force transmitted back on the pivot point.
Procedure: Make a estimate of where the “sweet spot’ will be located on the bat. Mark that point with a transparency marker. Use device shown in Appendix for this activity. Pull the bat back through a small amplitude and than release the bat (the amplitude should be less than 10 degrees. Determine the period of the bat (Time 10 complete cycles, back and forth, and than divide the time by 10 to determine the period T. Calculate the distance to the CP using the relation for a simple pendulum,
T = 2(L/g)1/2 or L = T2g/(42) where g = 980 cm/s2 = 9.80 m/s2
Data Table: t (s for 10 cycles) T (s) L (m)
Where in relation to the key spots (CM end) is the sweet spot? Measure and mark this point with the pen. Hold the bat at the pivot point and tap with hammer or other solid object (A baseball would work). Describe the feeling of the transmitted vibrations, and also the sound as various points on the bat are tapped.
Above and Beyond Design an experiment to determine the following: Set up the pendulum (bat) to collide with or hit small objects to demonstrate that the optimum impact occurs at the Center of Percussion. Where are the CM and CP of a tennis racket in terms of the geometric center of the racket head. Where are the CM and CP of a golf club. How does the amplitude (pull-back angle) affect the Period.
Station Four* Activity Six: COR – Baseball vs Turf
Objective: Determine the Coefficient of Restitution (the ‘bounciness) of a baseball under various conditions. Normal, Humid/Dry, Hot/Cold
Theory: The Coefficient of Restitution (COR) is a ratio of the velocity after an impact to the velocity − COR = 2f 1f − before the impact. 1 2 COR = f When object one bounces off a stationary object: i h COR = Since KE = ½ m 2 and PE = mgh H h = Bounce height, H = Drop height Materials: Meter stick, ball, drying oven, freezer, boiling water, strainer/steamer, Ziplock ® bags
Procedure: 1. Drop the ball from height range of 2.5 meters to 1 meter, onto a concrete floor/sidewalk/surface. (Use at least three heights, release three times each height) 2. Determine the bounce height 3. Repeat with balls with different characteristics: ie temperature, humidity
Analysis: Create a graph of Bounce height vs Drop height Calculate the slope of the graph Determine the square root of the slope.
Extensions: Repeat with variety of balls: Ping Pong, Tennis, Golf, Basket ball, Racket ball . . . Repeat with different stationary surfaces: tile floor, wood floor, aluminum slab, tennis racket, . . . Consider bounce off bat (metal/aluminum), bounce off turf (fielder’s concern)
At Target Field: Drop the ball onto the artificial turf, field turf.
Equipment: Ladder, Baseballs, Measuring stick, Artificial turf, Field turf
Theory: The Coefficient of Restitution (COR) is a ratio of: − C OR = 2f 1f − the velocity after an impact to the velocity before the impact. 1i 2i
When the object one bounces off a stationary surface: h COR = Since KE = ½ m 2 and PE = mgh H H = Drop height, h = Bounce height
Type surface Type ball Drop Height Bounce height COR H h h COR = H Concrete Super ball Golf ball Tennis ball Base ball Artificial turf Super ball Golf ball Tennis ball Base ball Target Field Super ball turf Golf ball Tennis ball Base ball
During Game at Target Field
Activity One during the game: Catcher’s Strongest Arm
This activity is to determine which catcher has the strongest arm. You will find the average velocity of the catcher’s throw as he throws the baseball from home plate to second base. The infielders on each team warm up between innings by fielding ground balls thrown by the first baseman and throwing them back to him. The catcher warms up by catching balls from the pitcher and finishing by throwing a ball down to second base, as if a baserunner were stealing. In this activity, you will record the time it takes for this throw to arrive at second base. Knowing the distance from home plate to 2nd, you can determine the average speed of the throw.
MATERIALS Stopwatch, calculator
PROCEDURE Calculate the distance from home plate to 2nd base. You know the infield is a square that is 90 feet on each side. Use the Pythagorean theorem to find the distance from home plate to second base.
A2 + B2 = C2 A and B are the 90 foot base lines (check to be sure these distances are correct).
Watch the players warm up between innings. As the time nears, the second baseman or the shortstop will stand on 2nd base. This will be your sign to be ready. Record the time the ball is in the air from the catcher to the player on 2nd base. Record in the table below. Repeat this procedure for the catcher from each team for three or four innings. Be sure to indicate in which inning you recorded your throw.
Distance from home to 2nd base (in feet):
Throwing Time, sec
Inning Team A Team B
ANALYSIS Calculate the speed of each catcher’s throw in each inning. Record your results in the table below.
Speed, ft/s
Inning Team A Team B
Determine the average speed of each catcher’s throw. Record.
Average Speed, ft/s
Team A Team B
QUESTIONS 1. Does the speed of the catcher’s throw change as the game goes on? Why or why not?
2. How do you think the strength of arm compares with other players on the team? Pick one or two other position players and compare.
3. In a real base-stealing situation, what other factors affect the time it takes the ball to get to second base?
Activity Two during the game: Hustle Award
Speed is an important part of the game of baseball. A pitchers success depends, in part, on the speed of his pitch. Players make sure that they keep their arm muscles exercised so that they can throw fast enough to help get the other team out. They continually practice running fast. How fast is fast? That is what this activity is about.
Purpose: Determine the speed of a batter as he runs from home to first base. Observe three different players.
Observations and Calculations: 1. What is the distance from home plate to first base (include units)? ______
2. Give the relationship for determining speed:
3. Determine the time for a runner to go from home plate to first base (be as accurate as possible since you get once chance for a player). a) Name of player ______
Time to run to first base: ______s Inning ______
Speed Calculation: Show the relationship with substitution with proper units.
Answer ______b) Name of player ______
Time to run to first base: ______s Inning ______
Speed Calculation: Show the relationship with substitution with proper units.
Answer ______c) Name of player ______
Time to run to first base: ______s Inning ______
Speed Calculation: Show the relationship with substitution with proper units.
Answer ______
Activity Three during the game: How Far Away Is That Batter?
If we know the speed of sound and we know the time it took that sound to travel from one point to another, we should be able to determine the distance between those two points. In this lab, we will try to determine our distance from the batter. Use 330 meters/second as the speed of sound.
PURPOSE: To determine the distance to the batter.
HYPOTHESIS: I think that the batter is about meters away.
PROCEDURE: 1. What is the formula for speed?
2. Rearrange this formula to find the distance.
3. Watch the playing field. As soon as you see the ball hit the bat, start counting the seconds until you hear the ‘crack’ of the bat. Repeat this 2 more times. (If you have a stop watch, use that.)
OBSERVATION: 1. Fill in the following chart:
Trial # of
seconds
Average # of seconds
2. Calculate the distance of the batter using the average number of seconds. Show all work including the formula and substitution. Don’t forget the units.
Answer
Activity Four & Five during the game: Whew! That Ball Seemed To Go Quite Fast! How Fast? Speed is an important part of the game of baseball. A pitcher’s success depends on the speed of his pitch. When baseballs are hit, they fly across the field at speeds we all envy. Players make sure that they keep their arm muscles exercised so that they can throw that ball fast enough to help get the other team out. And they continually practice running as fast as they can. But how fast is fast? We will find out.
PURPOSE A: To determine the speed of the first ball hit into the outfield by a player (the estimated speed off the bat not average speed)
OBSERVATIONS and CALCULATIONS:
1. What is the distance from home plate to where ball lands? ______(include units); this distance needs to be estimated.
2. Because you only get one time to do this, be sure to be as accurate as possible. Determine the time the ball is in the air (time from hit by bat until it lands in the outfield).
3. Give the relations needed to determine speed at an instant.
4) Speed off the bat is ______ANSWER
PURPOSE B: To determine the speed of the batter as he runs to first base.
OBSERVATIONS and CALCULATIONS:
1. What is the distance from home plate to first base? Include units.
2. Give the formula for determining speed.
3. Because you only get one time to do this for each player, be sure to be as accurate as possible. Time how long it takes for a player to run.
Name of player
Time to first base Inning
Speed Calculation. Show the formula and substitution. Don’t forget to put units on your answer.
Answer: ______
Activity Seven (at school/ or during the game: Work & Power
Objective:
The purpose of this activity is to investigate the amount of work and power required to raise a mass a vertical distance. Calculate the work done against gravity and power expended.
Theory: Work = (Force x distance)ll W = Fd(cos ) Force = Weight of the object F = mg Power = Work/time P = W/t
Materials: meter stick/measuring device, stop watch/timer, mass/object, stairway.
Procedure:
1. Determine the mass of the object. 2. Determine the height of the stairway. 3. Determine the time required to carry the object from the bottom of the stairway to the top. Measure the time twice, once when walking slowly and again for walking quickly.
Analysis:
Calculate the amount of work done for each trip in MKS units and in USCS units. Calculate the amount of power expended for each trip in MKS units and in USCS units.
Stadium information:
Determine the rise of the ramp to the seating area and the height of the steps. Determine the number of steps to assigned seat. Determine the time required to WALK (absolutely NO Running!) from the concourse to their assigned seat. Calculate the work and power to lift self from concourse to assigned seat.
Determine the calorie content of a Hot Dog – Assuming 70% efficiency, determine the number of times you would need to make the trip up the stairs to burn off that Delicious Dog!
Teacher NOTES:
Mass: OPTIONS . . .
1. Use a bathroom scale to determine the weight of each student’s backpack. (It is amazing how much weight these students carry around)
2. They can use their own weight. Give them the option of using a given (100 lbs) whatever if they are sensitive about their weight.
3. Borrow a “weight” from the weight room and have them lug that up the stairs.
4. A bowling ball . . .
Stairway: OPTIONS . . .
1. A flight of stairs in the school building.
2. The stairs for the bleachers of the high school football stadium . . . (Really sweet to blast the theme song for “Rocky” out the stadium speakers!)
3. Measure height of one step – count the steps
4. Count the number of concrete blocks and use that as a standard measure.
Analysis: 1 kg = 2.2 lbs (on Earth) 550 ft.lb/sec = ONE hp
Stadium information:
Students should have previously recorded standard height of concrete block. Students should record their seat number. Stopwatch, cell phone timer, Ipod timer . . . to measure the time it takes to WALK to their seat. Emphasize absolutely NO running. 1 Calorie = 1000 calories = 4186 Joule
APPENDIX
ABBREVIATIONS: CM = Center of Mass CO = Center of Oscillation COR = Coefficient of Restitution CP = Center of Percussion
Constants and conversions ag = 980 cm/s2 = 9.80 m/s2 = 32 ft/s2
Recall 1 meter = 3.25 ft
1 kg = 2.2 lbs (on Earth) 550 ft.lb/sec = ONE hp
1 Calorie = 1000 calories = 4186 Joule
Dugout to Home Plate to Home Plate to Left Center Right Field Foul line First & Third Pitcher’s Field Field Base Mound 51 feet 90 feet 60 feet 6 339 404 328 feet inches feet feet
Target Field
a) COR = The rules of baseball state a legal baseball traveling at 60mph at a wall of northern white ash must rebound with a speed of 54.6 ± 3.2% of the initial speed. This number, 0.546, is called the “coefficient of restitution,” or COR, Since the COR is the ratio of the outgoing speed to the incoming speed, you can measure it by finding the square root of the ratio of the heights. Theory: The Coefficient of Restitution (COR) is a ratio of the velocity after an impact to the velocity − COR = 2f 1f − before the impact. 1 2 COR = f When object one bounces off a stationary object: i h COR = Since KE = ½ mv2 and PE = mgh H Where h = Bounce height, H = Drop height b) CP = center of percussion The center of percussion is the point on an object where a perpendicular impact will produce translational and rotational forces which perfectly cancel each other out at some given pivot point, so that the pivot will not be moving momentarily after the impulse. The same point is called the center of oscillation for the object suspended from the pivot as a pendulum. Centers of percussion are often discussed in the context of a bat, racquet, sword or other long thin objects. The center of percussion may or may not be the "sweet spot" depending on the pivot point chosen. The sweet spot on a baseball bat is generally defined as the point at which the impact feels best to the batter (it is also occasionally defined as the point at which the maximum velocity is imparted to the ball, but this may not be the same point).
Although it has long been believed the center of percussion and the sweet spot are the same, recent practical observations have indicated that the point many batters feel is "sweetest" corresponds to a pivot point in the arm, beyond the handle of the bat. For the baseball activities in the student workbook we will assume the effective length from the pivot point of the bat acting as a pendulum will be the “sweet spot.”
T = 2(L/ag)1/2 Or L = T2ag/42
Where T = period; ag = acceleration due to gravity; L – effective length of bat; and = pi or approximately 3.14
c) CO
d) Center of Mass (CM) or (center of gravity) of an object is the point where the object's mass distribution is centered.
Activity 1 and 2 Teacher Notes
1) Compare the average value of reaction time determined by doing the Exploratorium method with the average using the dropped bat method.
Reaction Time Using Exploratorium Method Trial number Reaction Time (s) Average Reaction Time 1 2 3
Reaction Time Using Dropped Bat Method Trial number Reaction Time (s) Average Reaction Time 1 2 3
2) Have students compare the reaction times in Activity 1 and 2 with the time it takes a baseball traveling 90 mph to travel 60’6” which is the distance from the pitchers mound to home plate.
Time = distance/speed = 726 in/1504 in/s = .483 s
3) Activity 2 can be done at different levels: a) Elementary or physical science students might find the average distance the bat drops and than use the chart on the next page to determine the average reaction time.
b) Physics students should be able to substitute the average distance the bat drops into the relation distance = ½ *acceleration due to gravity * (time) 2 where they first solved the relation for time time = square root of(2 * distance divided by acceleraltion due to gravity).
c) the time reaction chart is on a separate page to make it easier for making a copy for students.
Chart For Determining Reaction Time to Catch A Dropped Bat
DISTANCE TIME DISTANCE TIME DISTANCE TIME DISTANCE TIME (cm) (sec) (cm) (sec) (cm) (sec) (cm) (sec)
0.012 -- 0.005 8.281 -- 0.130 31.862 -- 0.255 70.756 -- 0.380 0.049 -- 0.010 8.930 -- 0.135 33.124 -- 0.260 72.630 -- 0.385 0.110 -- 0.015 9.604 -- 0.140 34.410 -- 0.265 74.529 -- 0.390 0.196 -- 0.020 10.302 -- 0.145 35.721 -- 0.270 76.452 -- 0.395 0.306 -- 0.025 11.025 -- 0.150 37.056 -- 0.275 78.400 -- 0.400 0.441 -- 0.030 11.772 -- 0.155 38.416 -- 0.280 80.372 -- 0.405 0.600 -- 0.035 12.544 -- 0.160 39.800 -- 0.285 82.369 -- 0.410 0.784 -- 0.040 13.340 -- 0.165 41.209 -- 0.290 84.390 -- 0.415 0.992 -- 0.045 14.161 -- 0.170 42.642 -- 0.295 86.436 -- 0.420 1.225 -- 0.050 15.006 -- 0.175 44.100 -- 0.300 88.506 -- 0.425 1.482 -- 0.055 15.876 -- 0.180 45.582 -- 0.305 90.601 -- 0.430 1.764 -- 0.060 16.770 -- 0.185 47.089 -- 0.310 92.720 -- 0.435 2.070 -- 0.065 17.689 -- 0.190 48.620 -- 0.315 94.864 -- 0.440 2.401 -- 0.070 18.632 -- 0.195 50.176 -- 0.320 97.032 -- 0.445 2.756 -- 0.075 19.600 -- 0.200 51.756 -- 0.325 99.225 -- 0.450 3.136 -- 0.080 20.592 -- 0.205 53.361 -- 0.330 101.442 -- 0.455 3.540 -- 0.085 21.609 -- 0.210 54.990 -- 0.335 103.684 -- 0.460 3.969 -- 0.090 22.650 -- 0.215 56.644 -- 0.340 105.950 -- 0.465 4.422 -- 0.095 23.716 -- 0.220 58.322 -- 0.345 108.241 -- 0.470 4.900 -- 0.100 24.806 -- 0.225 60.025 -- 0.350 110.556 -- 0.475 5.402 -- 0.105 25.921 -- 0.230 61.752 -- 0.355 112.896 -- 0.480 5.929 -- 0.110 27.060 -- 0.235 63.504 -- 0.360 115.260 -- 0.485 6.480 -- 0.115 28.224 -- 0.240 65.280 -- 0.365 117.649 -- 0.490 7.056 -- 0.120 29.412 -- 0.245 67.081 -- 0.370 120.062 -- 0.495 7.656 -- 0.125 30.625 -- 0.250 68.906 -- 0.375 122.500 -- 0.500
Activity 5 teacher notes Construction of device used to determine one of the “sweet spots” of a baseball bat: the center of Percussion (CP) using a bat as a pendulum.
Materials: Wood block – 4.0” X 4.0 “ X 0.5” (2.25 “ diameter hole drilled and with 2 – 1/8” holes on middle sides to allow pivot point) A 7” straight section from metal coat hanger wire bent approximately 1” from one end at 90o angle (this is the pivot point; it goes through block and bat) Ring and ringstand that can be clamped to edge of table to allow a bat suspended to rotate freely Wood bat with 1/8” hole drilled between normal hand position Duct tape to secure block-bat device to ring and not interfere with normal pendulum swing; duct tape can also secure short end of wire to block
bat pendulum device for determining CP materials for bat pendulum device