18 Force and Motion II
Name: _________________________________________
Date: _______________________
Partners:____________________________________________________________
Equipment
|
|
I. Dueling Force Sensors
Open the file TwoForces.
Set each sensor to the ±10 N setting and securely attach it to the top of a cart. Place the carts at rest on the track.
Calibrate both sensors by selecting Experiment/Calibrate and then selecting either sensor. On the pop-up menu, check both sensors and select Calibrate Now. You will now perform a two-point calibration of both force sensors:
- For the first calibration point, do not apply any force to the sensors, enter 0 N, and hit Keep.
- For the second calibration point, hang a 200 g mass from each sensor. Enter the weight of this mass (1.96 N) and hit Keep.
When complete, place both sensors back on the track and zero both force sensors.
Connect the force sensors by a short loop of string. Press Collect and pull first on one cart and then the other. Sometimes hold the other cart in place and sometimes let it roll freely. Don’t go crazy; keep the forces under 10 N.
Question: Describe the relationship between the two measured forces.
Replace the string with a rubber band. Press Collect and pull on both carts, then one and then the other. Sometimes hold the other cart in place and sometimes let it roll freely.
Question: Describe the relationship between the two measured forces.
Replace the rubber band with a rubber bumper. Press Collect and push on both carts, then one and then the other. Sometimes hold the other cart in place and sometimes let it roll freely.
Question: Describe the relationship between the two measured forces.
Question: Why are the forces displayed not equal in magnitude and opposite in direction? What algebraic sign does the sensor give to “pulls”? To “pushes”?
II. A Train
Create a “train” of two carts. The rear cart, closest to the motion detector, should be connected to the front cart by a short loop of string from the hook of the force sensor to a fixed point on the front cart.
The front cart should be attached to a 200 g mass by a string that passes, from the force sensor hook, over a pulley. Thus, you will measure both the force between the two carts and the force applied to the front cart.
Hold the rear cart in place about 20 cm in front of the motion detector, press Collect, and after about 1 second of data collection release the cart. Make sure that the force sensor cords do not drag behind the carts nor trigger the motion detector. Repeat until you have clean data.
Question: As you saw in a previous activity, your force vs. time graphs show a clear decrease in force when you released the cart. However, one of the forces decreases by a substantially larger amount than the other. Clearly explain which force decreases by the larger amount and why this larger decrease occurs. (It’s probably useful to use Newton’s Second Law in your explanation.)
Question: Imagine adding a 500 g mass to one of