PHYS 1405 Conceptual Physics I Galileo s Hot Wheels Leader: Skeptic: Recorder: Encourager: Materials 4 lengths Hot Wheels TM track (2 long, 2 short) 2 Meter sticks 3 Track connectors Tape measure 1 Hot Wheels TM clamp Masking Tape 1 Hot Wheels TM car 1 Paper Clip 2 Ring Stands (1 stationary, 1 moveable) 2 Right Angle Clamps 2 Jaw Clamps Introduction While awaiting trial for the publication of his book supporting the heliocentric model of the solar system, Galileo turned his attention to the study of motion. He studied motion by rolling balls down planes and making clever measurements of the time it took the balls to roll down the planes. (Stop watches wouldn t be invented for centuries.) In this activity we will conduct one of Galileo s experiments using Hot Wheels TM instead of a ramp and ball. Figure 1. View of the entire experimental set up. Phys1405, Galileo s Hot Wheels v. 3, p 1/1
Procedure 1. Set-up Place the ring stands about 1 m apart on the table. Position one right angle clamp on each of the ring stands about 50 cm up above the tabletop. Attach the Hot Wheels TM clamp to the jaw clamp on the stationary ring stand. For convenience we will refer to the section of track between the Hot Wheels TM clamp and the table top as the Start Ramp and the section of track between the tabletop and the moveable ring stand as the End Ramp. Figure 2. View of the Hot Wheels TM clamp and Start Ramp mounted on the stationary ring stand. Figure 3. View of the End Ramp with the meter stick taped to the bottom of the track mounted on the moveable ring stand. The track just rests on the opposite end of the jaw clamp. Phys1405, Galileo s Hot Wheels v. 3, p 2/2
Figure 4. Method for applying tape to the track Connect together the provided pieces of track. Attach one end of the track to the Hot Wheels TM clamp mounted on the stationary ring stand (See Figure 2.). On the End Ramp section of the track you will attach a meter stick to the backside of the track with masking tape to support it and then rest this section of the track over the clamp on the second (moveable) ring stand (See Figure 3.). In the center of the track, where it touches the table top you need to anchor it to the table. Place a loop of masking tape, sticky side out, under this portion of the track and press it down to the table. Next take a strip of masking tape about 6 inches long and place it across the track, perpendicular to the direction of the track. Carefully press it down so that it follows the contour of the track and sticks tightly to the table. Now you need to remove the portion of the tape that is covering the track where the Hot Wheels TM car will be traveling. Use the end of a straightened paper clip to score the masking on the inside of the track where the sidewall meets the flat portion of the track. Remove this portion of the masking tape covering the flat part of the track. (See Figure 4.) Any tape covering the flat portion of the track should be removed in this manner. Mark the point where the track touches the table top with a piece of masking tape. You will be measuring your length of travel distance from this point. 2. Adjustments We will release the car from the Start Ramp side of the track that is attached to the Hot Wheels TM clamp. Use the meter stick to measure the height above the table from which the car is released. In measuring the car height, both on the Start Ramp and on the End Ramp, we will be measuring from the table surface to the highest portion of the car. On the Start Ramp this will be the back of the car and on the End Ramp this will be the front of car. Phys1405, Galileo s Hot Wheels v. 3, p 3/3
You should measure the height to the nearest millimeter (mm). When you record any measurement you should include the unit with which it was measured. Now we need to pick the height of the release point to accommodate all the measurements we want to take. Adjust the track on the End Ramp so that it is about 10cm above the surface of the table where it is resting on the support rod. Release the car from the Start Ramp at various heights and note how far it travels on the End Ramp. You want a release height that will take the car almost to the end of the End Ramp but not past the end of the End Ramp. When you have found this release height enter the value below and mark this location of the car height on the Start Ramp with a piece of masking tape so that you will be able to release the car from the same height each time without having to measure it before each trial. Height of release point: 3. Acquire Data Now raise the support bar under the End Ramp so that the track is about 50cm above the table at this point. Release the car from the top of the Start Ramp and observe the highest point to which it rises on the End Ramp. Use the meter stick to measure the height above the table the car reached on the End Ramp. Also measure with the tape measure the length along the End Ramp to the highest point reached by the car. You should measure this length from the spot on the table you marked with tape. Record your data in the data table in the row for Trial 1. Data Table Trial Height above Table Length along the End Ramp 1 2 3 4 5 Move the clamp supporting the End Ramp down by 10 cm. Release the car from the same starting position. Observe the highest point to which the car rises on the End Ramp and then measure the height above the table of that point as well as the length along the End Ramp. Record your data in the data table in the row for Trial 2. Repeat the above experimental procedure after lowering the clamp supporting the End Ramp by 10 cm three more times. Record in the data table the height above the table and the length along the End Ramp of the highest point to which the car rises. Phys1405, Galileo s Hot Wheels v. 3, p 4/4
Questions 1) Initially the angles made by the Start Ramp and End Ramp with the table top were approximately the same. As you moved the End Ramp support rod lower, how did the angle of the End Ramp change compared to the angle of the Start Ramp? Explain. 2) Based on your data in the data table, did the maximum height reached by the car change significantly as you moved the End Ramp lower? Explain. 3) Ideally, the car should reach the same height from which it was released. What effects might keep the car from reaching that height? 4) As you lowered the angle of the End Ramp, how did the distance the car traveled along the End Ramp change. 5) If you were to continue lowering the angle, how would you expect the distance the car traveled along the track to change? 6) How far would you expect the car to travel along the track if the End Ramp were flat? Explain. 7) Galileo used this reasoning to arrive at the law of inertia. Complete the following, If we can ignore an object in motion will. Phys1405, Galileo s Hot Wheels v. 3, p 5/5