Jumping Bridges Game (Good for Time at 2)

Gravity Notes

Intro - The first screen shows three spaceships of different size all with the same size rockets. Then there is some text describing how gravity is a force just like the rockets and that we will be studying this attractive force that exists between objects. Contents - Describing gravity - Air Resistance - Feed the monkey - Jump the lagoon (v = at) - Cross the bridge (d = ½ at2) - Analysis Describing Gravity - Show three balls of different mass and ask the students to predict how they will behave when dropped. o Each ball will fall the same way. o The heavier ball will fall faster. o The lighter ball will fall faster. - Show them a comparison between two worlds each with a set of ball. One world has no gravity the other does. They are then asked to run the simulation and are asked if the balls with no gravity behaved as expected and to explain why they don’t move at all. - Then they are given the ability to put forces on the no gravity balls to simulate gravity. They can ask for hints if they can’t get the balls to behave just like the ones in the world with gravity. When they get it right they are automatically taken to the next node. - They are then asked to explain why setting up the forces in the way that they did worked. They are then told that objects in space don’t have weight but do have mass, and that weight has to do with the force of gravity. They are then asked to postulate as to why the ball with the most mass will also be the heaviest. - They are then asked to come up with a way to tell how much mass something has if they were a scientist on the International Space Station and couldn’t put the object on a balance or scale. - They are then given a way to record data about the balls as they fall. The tables show time, position, velocity, acceleration, mass, and force. Near the surface of the earth gravity can be represented by a constant value. Which of the values recorded remained constant AND was common to all of the balls. (Give them a multiple-choice list to choose from.) - Yes, the best way to talk about gravity is the acceleration it gives to objects. All objects are accelerated the same amount. Explain why all objects have the same acceleration. (Hint: look at the forces you associated with each object.) How can you figure out the acceleration by doing some calculation with the force and mass? - Show two balls, one with an initial velocity in x direction. Have them predict if they think both balls will hit the ground at the same time. (multiple choice – yes, or no) Explain their prediction. Then try it. If they were wrong, ask them to explain why after the test. Air Resistance - Introduction about the limitation of models. Have them drop the three balls again and point out anything that seems “weird” or incorrect with the computer model. - Ask students to stand up and drop a hammer and a feather at the same time (paper and pencil can be substituted). Then ask them to describe the results of their experiment. They can then drop a virtual hammer and feather using our computer model. Afterwards they are asked to compare the two experiments. - Show movie of moon hammer/feather drop and student feather/hammer drop. Why does model work for moon but not Earth. What do we have on Earth that they don’t have on the moon? - Show a simulation that allows them to change the air resistance of a simulated hammer and feather on both the moon and Earth. Tell them the model will now allow them to add air resistance to the model to make it more “real”. Ask them if this is a better model than the one we had before. Is there still anything wrong with it? - Show two scenarios where they can pick various environments, things to drop, and properties to graph. Ask them to experiment with this to determine the effect of air resistance on the motion of a falling object. Questions: “In general how does air resistance affect a falling object? Describe what you see visually, and how the graphs of distance, velocity, and acceleration match your description.” “Why does air resistance seem to affect some objects more than others?” “What is the relationship between the velocity and acceleration of an object? Is that relationship any different with or without air resistance?” “Terminal velocity is when something falls through the air with constant velocity. What would be the acceleration for an object that has reached terminal velocity?” - Air resistance is a form of friction. To better understand air resistance let’s study something for which air resistance is crucial for survival – parachute jumping. Let’s start with someone who accidentally forgot his parachute. Push play to see him jump and create graphs of his velocity and acceleration. “Is air resistance having any affect on his motion? How can you tell? (Hint: the graphs are important. If you don’t know what to look for go back and do more experiments with falling objects. Try the same object with and without air resistance.)” - Arrows representing the force of gravity and the force of air resistance will now be displayed. Describe what happens to the force of gravity and of air resistance as the jumper flies through the air. At some point the sky diver reaches terminal velocity. Using both the graphs and the force arrows, how can you tell when this happens? - After hitting the ground pretty hard, he realized that he should be using a parachute. Run the simulation again and observe what happens. “How does using a parachute affect reaching terminal velocity? Why? - To the right is the parachute jumper. Your challenge is to get him to land as quickly as possible, but he must not exceed a certain velocity when he lands. The blue lines on the graph represent the range of velocities that are acceptable for safe landing. You have two options for slowing him down, a large parachute and a small parachute. To use either one drag the small and large parachute arrows from the bottom of the screen to indicate when to use the small and/or large parachute. (Let them try, giving them hints if necessary. If they do land safely challenge them to do it in a faster amount of time.) At the end ask “Explain your strategy for success, by describing how you used the different parachutes to affect the velocity, acceleration, and forces on the jumper.” Feed the Monkey - Now you are a zookeeper at a zoo with a very fussy monkey. This particular monkey likes to hang on trees, and refuses to eat unless he is tossed a banana. If you miss tossing him the banana more than twice in a row, the monkey will starve, so think before you try throwing the banana. First let’s try it as if there were no such thing as gravity. Try throwing the banana from three different locations. (Proceed when they hit the monkey three times.) What did you have to do to make sure the monkey got the banana? - The monkey, seeing that you are getting too good at that game, decides that he is going to drop from the tree when he sees you throw him a banana. Try throwing the banana from three different locations. (Proceed when they hit the monkey three times.) What did you have to do to make sure the monkey got the banana? Was this harder or easier than you thought it would be? Why does aiming the banana right at the monkey still work when gravity is turned on? - OK. Now the monkey has become really fussy. He will only catch the banana if it is at the peak of its throw where Vy = 0. This time he is going to hang on to the tree. Remember if you miss the monkey three times he will starve, so think before you try. - The monkey is almost full. If you feed him one more banana, he will be very happy. However, he will only catch the banana if you toss it to him so it reaches him just as he reaches the ground. He will reach the ground 5 seconds after letting go. Jump the Lagoon - As you have seen, when something falls it speeds up, and keeps speeding up if there is no air resistance or other forces on that object. To complete your next set of challenges you must understand how fast something will be going if it has fallen for a certain amount of time. This involves understanding the relationship between velocity, acceleration, and time. Run the experiment and explore the data to see if you can come up with a way to calculate V by using the numbers for acceleration and time. - You begin an adventure, trekking across the wilderness when you come across a deep gorge. You need to cross it and end up much lower than where you started. The velocity boosters have been placed for you at levels where you will be after falling for one second, two seconds, and so on, but they won’t work unless you can predict what velocity you will have in the Y direction when you pass over the booster. Type in the appropriate prediction for each booster to activate it. - On you next adventure you have gone to a different place where the acceleration of gravity is only 0.5 cm/sec^2. Again you must cross this gorge. When they complete the challenge ask. Explain how you were able to make your predictions about crossing each of the gorges. - Back in your normal environment where the acceleration is 1.0 cm/sec^2 you come to a river. Fortunately, someone has left you a bunch of magic velocity boosters on this side of the river. Place the velocity boosters such that you hit all of them and make it to the other side of the river (the right side of the screen). (Do a couple of levels of these.) - If a ball is tossed into the air which statement is true about that ball: o The ball has a force that decreases as it reaches its peak. o The force of gravity only pulls on the ball on its way down. o The force of gravity pulls on the ball at all times. o The force of gravity pulls on the ball at all times, except for the moment that the ball is stopped at its peak. Explain why you think this. Cross the bridge - In order to complete the next challenges, you will have to figure out how far something will fall in a certain amount of time. Run the experiment and see if you can figure out how to calculate the distance something will fall by using only the numbers from the acceleration and time. - Here you have a bridge. You can only proceed to the next section of bridge if you can open the door. To open the door you need to drop the ball under each section of bridge so that it hits a key below it. However, the ball will only fall for the number of seconds listed on the ball, so you must place the key at the location where the ball will stop falling. - Variation on the above with different gravity. - Variation on the above with different starting locations for the bridge sections.