7/27/2019 z Accelerating Cart

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The Accelerating CartMicrocomputer-Based Lab

In this experiment you will investigate the connection between the net force applied to acart on an inclined track and the acceleration of the cart.

PROCEDURE

For this experiment you can use the software from the Position, Velocity, andAcceleration experiment. The only sensor used in this experiment is the ultrasonic motionsensor, which should be mounted on one end of the track.

1. Incline the track by placing a black bar under one pair of the tracks supporting legs. It isbest if the motion sensor is at the highest point. Use the height of the black bar, which youcan measure with vernier calipers, to help you find the angle at which the track is inclined.

Question 1: Describe how you will determine the angle at which the track is inclined. Whatelse do you need to measure? Show how you combine your measurements to find the angle.

2. Release the cart from rest and record the carts motion as it accelerates down the track.

3. On the velocity graph, click and drag with the mouse to select a region in which the cart hasan approximately constant acceleration down the track. Press the Regression button, , todo a straight-line fit to determine the carts acceleration (this is the slope of the straight-linefit). It is a good idea to repeat this measurement a few times to get an average value of thecarts acceleration down the slope, as well as to get a feel for the uncertainty in yourmeasurement.

4. Draw a free-body diagram showing the forces acting on the cart as it accelerates.

5. It is often convenient to choose a coordinate system so the acceleration is parallel to one ofthe coordinate axes, giving no acceleration along the other axis. Aligning your coordinatesystem with the direction of the carts acceleration, break the forces on your free-bodydiagram into components that are parallel to your coordinate axes.

6. Determine an expression for the net force acting on the cart. This should depend on one ormore of the following: m, the mass of the cart; g, the acceleration due to gravity; and , theangle at which the track is inclined.

7. Use Newtons Second Law to determine a predicted value for the carts acceleration.

Question 2: How does the value you measured for the acceleration in step 3 compare to the

value you predicted the acceleration should be based on your free-body diagram? Do yourtwo values show reasonable agreement? If you observe a discrepancy see if you can come

up with one or more possible explanations for it.

8. Change the angle of the track (stacking up additional black bars is a convenient way to dothis) and repeat the experiment. Do this as many times as you have time for.

1 The Accelerating Cart