Physics 1405: Conceptual Physics I Name(S)______

Physics 1405: Conceptual Physics I Name(s)______

Newton’s 2nd Law of Motion

Equipment Air track with accessory box, smart pulley, string, mass hanger with masses.

Discussion The purpose of this experiment is to investigate Newton's 2nd Law of Motion. A small mass (m) will hang over a pulley at the end of the airtrack and will pull a cart of mass (M) along the length of the airtrack. It can be shown from Newton's 2nd Law that the acceleration a is given by the equation:

mg a = Equation 1 (M+m)

where mg is the force (weight) on the system that is made up of the cart and hanging mass.

Figure 1

Procedure

1. Set up an airtrack with a smart pulley at one end. Balance the airtrack by turning the air on and placing the glider in the middle of the airtrack. Adjust the legs of the airtrack so that the glider barely moves.

2. Ask the instructor or lab attendant how to locate the proper file on the computer for your sensor.

3. Attach the hook accessory to one end of the cart. Balance the cart by adding some other accessory on the other end of the cart. (See photo in Figure 1). Weigh the cart. Record this in kg.

4. Attach a string (about 1.5 m) to the hook on the cart. Have the string go over the smart pulley and hang down, ready to be attached to a weight hanger at the other end. Make sure that the string is parallel to the airtrack.

5. Attach a hanging mass (m) of 0.025 kg to the string. You can use any masses available. Make sure to measure the hanging masses to be sure they are about 0.025 kg.

6. This step works best with 2 people. One will move the cart backwards until the hanging mass hanger almost touches the pulley. The other person will click the Collect button (or press Return).

Cavalli 2008 1 The first person will release the cart. The mass hanger will fall downward and pull the cart across the air track. (Catch the cart before it hits the end of the airtrack so that no damage is done.) Click the Stop button or press Return to stop timing before the mass reaches the end of the track.

7. The computer will then display a set of graphs. Look for the Velocity vs. Time graph. The slope of this graph is the acceleration of the system. Next, go to Analyze on the menu bar and go down to Linear Fit. The computer will then display a linear equation from which you can get the slope. The value of slope is your experimental acceleration.

8. Using equation 1, compute the accepted acceleration. Compare the theoretical acceleration (found from equation 1) with the actual measured acceleration and calculate a % error.

A  E % Error = x100 = A

9. Repeat the entire process with other mass combinations as shown in the Data Section.

Keep the cart mass the same and change the hanging mass for Parts a) and b).

Part a). Hanging Mass One, m = ______kilograms

Mass of cart, M = ______kilograms

Total mass, (M + m) = ______kilograms

Net force, mg = ______Newtons

mg Accepted acceleration, = ______m/s2 (M  m)

Experimental acceleration = slope of velocity vs. time graph ______m/s2

A  E % Error = x100 = ______% A

Cavalli 2008 2 Part b). Hanging Mass Two, m = ______kilograms

A  E % Error = x100 = ______% A

Increase the mass of the cart and then repeat the above procedure for Parts c) and d).

Part c). Hanging Mass, m = ______kilograms

A  E % Error = x100 = ______% A

Cavalli 2008 3 Part d). Hanging Mass, m = ______kilograms

A  E % Error = x100 = ______% A

Analysis and Discussion

1. List all the possible source of experimental error. Be specific.

2. In the experiment, should the mass of the string be added to the total mass moved by the unbalanced force for better accuracy? Explain.

Cavalli 2008 4 3. Complete the following sentences:

a. When the unbalanced force increases (total mass remaining constant), the acceleration of the system ______.

b. When the total mass that is accelerating increases (unbalanced force remaining constant), the acceleration of the system ______.

Cavalli 2008 5