Puck Compared to a Ball: Size & Shape

Objective To discover why a puck is shaped differently than a ball while also providing an opportunity to practice math computations.

Materials Softball, hockey puck, baseball, tennis ball, racquetball, drinking straws, masking tape, stopwatches

Estimated Time 35 minutes (This is provided as a guide, as all activities can be lengthened or shortened as necessary)

CA State Science Standards 3rd grade I&E5c, d, e; 6th grade I&E6 c, f; 5th grade I&E6f, g

Video Support Content None Available

The Science Newton’s First Law of Motion: An object at rest will remain at rest unless it is acted upon by an unbalanced force. A moving object will continue to move at a constant rate and in the same direction unless it is acted upon by an unbalanced force. Newton’s First Law of Motion Explained A non-moving puck will stay in one place forever without moving, unless a force acts upon it, such as being hit with a hockey stick or someone picking it up, etc. But once the puck starts moving, it will move with the same speed and in the same direction until another force, such as gravity, air resistance, friction, or a force by a 220- pound (100 kg) hockey player slows, speeds up, changes the direction, or stops the puck.

Newton’s Second Law of Motion states in general that the acceleration of an object depends upon two variables - the force acting upon the object and the mass of the object. In other words, it requires more force to get a heavier resting object to move or to stop once it is in motion, than a lightweight object to move or to stop once it is in motion.

Student Activity Extend and apply the information learned in Activity 2 - Introduction to Newton’s Laws while discovering why pucks are especially shaped the way they are. Have the students compare the difference in the design of balls that are used in most sports with a puck. [The sports balls are sphere-shaped (students might discuss the materials they are made of, such as leather, felt or rubber) whereas the puck is a short, wide column-shaped piece of solid rubber.]

Display each of the objects listed below and ask the students to guess (without touching the objects) the order of the objects from heaviest to lightest in weight. Place the objects in the students’ suggested order of heaviest (first) to lightest (last). Then using the chart below, change the placement of the objects on display, if necessary, to show the actual order of the objects from heaviest to lightest in weight. Ask the students to notice the diameter of the objects, then ask if they believe that the objects are lined up according to the width of their diameters (the longest to the shortest in width). In fact, the heaviest object has the greatest diameter [the softball] and the lightest weight object has the shortest diameter [the racquetball], with the exception of the hockey puck and the baseball which have the same diameter.

Math Activity To practice the students’ math skills, have them convert the weight (ounces) and diameter (inches) of the objects below into International units. Write on the whiteboard that 1 ounce = 28.3 grams and 1 inch = 2.5 centimeters, then have the students multiply and record their answers on a similar chart as shown below.

Weight Diameter Weight Diameter Object (ounces) (inches) (grams) (centimeters)

Softball 6.8 3.75

Hockey 6.0 3.00 Puck Baseball 5.0 3.00 Tennis Ball 2.0 2.50 Racquetball 1.4 2.25

Unit Conversions for Items Above Softball = 190.4 g, 9.4 cm Hockey puck = 168 g, 7.5 cm Baseball = 140 g, 7.5 cm Tennis Ball = 56 g, 6.25 cm Racquetball = 39 g, 5.6 cm.

In Activity 2, we discovered that the heavier ball required more force to start moving and therefore was slower at crossing the finish line (if at all), whereas the lightest weight ball started moving immediately and traveled quickly across the finish line with little force required. Will the weight and/or the diameter of the objects below affect the speed at which they travel when blown by the students as in Activity 2? [The weight and diameter of the objects will affect the rate at which they travel. If all of the students blow with an equal force, the heaviest ball will be last across the finish line and the lightest weight ball will be the first across the finish line. However, the puck will not move, although it is not the heaviest object.]

Line up the objects as before on a masking tape start line, and then have students volunteer to blow through drinking straws to provide the force necessary to move the objects across the masking tape finish line. As in Activity 2, have other volunteers use stopwatches to determine the amount of time it takes for the objects to cross the finish line. Signal the start of the race, time each of the balls from start to finish, then calculate the speed [speed is equal to the distance divided by the time it takes to travel that distance] and discuss the results of the race.

Object Mass (g) Distance (m) Time (s) Speed (m/s) Hockey Puck Softball Baseball Tennis Ball Racquetball

Did the objects travel farther/faster in relationship to their weight? [If all of the students blew with an equal force, the heaviest ball will be last across the finish line and the lightest weight ball will be the first across the finish line.]

Which object traveled the least distance? [The puck which did not move at all.] Do you think this was due to its weight? [No, in this case, the shape of the object was a determining factor.]

Hockey used to be played with a ball, but it evolved into a puck-shape. Why do you think this was important? [The puck-shape allowed for increased surface area rubbing against the ice compared to a sphere-shaped ball. The increased surface area of a puck, along with the material of which the puck is made (rubber) increased the amount of friction and, therefore, provided better control on icy surfaces.]

Activity 3: Puck Compared to a Ball: Size & Shape

To practice your math skills, convert the weight (ounces) and diameter (inches) of the objects below into International units. 1 ounce = 28.3 grams, 1 inch = 2.5 centimeters

Multiply and record your answers on the chart below.

Object Weight (ounces) Diameter (inches) Weight (grams) Diameter (centimeters)

Softball 6.8 3.75

Hockey Puck 6.0 3.00

Baseball 5.0 3.00

Tennis Ball 2.0 2.50

Racquetball 1.4 2.25

Race Time! Record the distance and time for each of the balls from start to finish, then calculate the speed [speed is equal to the distance divided by the time it takes to travel that distance].

Object Mass (grams) Distance (meters) Time (seconds) Speed (meters/seconds)

Softball

Hockey Puck

Baseball

Tennis Ball

Racquetball

Which object traveled the least distance? Do you think this is due to its weight?