Force and Acceleration
Lab Experiment

Objectives
To practice drawing force diagrams and solving force problems using Newton's 2nd Law (Fnet = ma). To predict and measure the acceleration of a cart on a tilted air track.

Equipment
Air track, cart, stopwatch, lab jack.

Procedure
Background

Read the abstract of the paper "Acceleration on an Inclined Plane" by DB Floogle and JW DePew for background theory. You will be testing Floogle and DePew's result.

Experiment

  1. Level an air track on your lab bench and measure the distance L between the feet of the track. Then put the single-foot end of the track onto a lab jack and raise the jack so the track angle is 3.5o. (Hint: sketch the triangle under the track and note that the required height of the raised foot is h = Lsin(theta)).
  2. Predict the acceleration of the cart for the 3.5o angle using Floogle and DePew's theory.
  3. Release the cart from rest and measure the time t it takes to travel the distance x to the end of the track. Repeat 10 times and determine the mean time (M) and its uncertainty (SD). Be sure that each partner makes some of the time measurements, and average all partners' data together.
  4. Use an appropriate kinematics equation to calculate the experimental acceleration from your x, vo and t data.
  5. Find the discrepancy between the measured and predicted accelerations. Is the discrepancy significant?

Force Diagram

  1. Draw a sketch of the cart on the track and identify the forces acting on it. Choose a coordinate system oriented with the x-axis parallel to the track and draw the force diagram for the cart.
  2. Write the x-and y-components of the forces and acceleration in a table, then generate an appropriate force equation using Newton's 2nd law and solve it algebraically for a, the acceleration of the cart.
  3. Do you obtain the same formula as Floogle and DePew? If not, use your equation to predict an alternate theoretical acceleration and compare it with your measured result.

Class Results

  1. Write your group's measured acceleration on the board.
  2. When there are at least 6 reported values written on the board, find the class mean and standard deviation. Compare the class results with predictions.