Newton’s Second Law Lab

Purpose

To model data with Newton’s Second Law.

Prelab

1. Write the equation of Newton’s Second Law of Motion.
2. If a plot is made of Force (on the y-axis) versus acceleration (on the x-axis), what will the slope of the line be?

Part 1 - PhET Simulation

Materials

• An internet connected device
• stopwatch

Procedure

1. Open up the PhET Forces and Motion Basics Simulation.
2. Choose “Motion” from the menu.
3. From the menu, check the box next to speed. A speedometer will appear. Each major tick mark is 5 m/s.
4. Check the box next to masses, and record the mass of the object you are using.
5. Use the right arrow to start a force on the crate while simultaneously start your stopwatch. Time how long it takes for the crate to reach 50 m/s (the maximum value on the speedometer).
6. Record the force and time in the data table.
7. Repeat steps 4 and 5 for forces of 100, 150, 200 and 250 Newtons.

Data

Object Mass (kg):

Analysis

1. Use the time you measured during the lab to calculate the acceleration of the object. Remember that

acceleration = change in speed / time

2. Make a plot of Force vs. Acceleration.

3. Put in the best fit line and find the slope.

Conclusion and Evaluation

1. Does the simulation follow Newton’s Second Law? How do you know?

2. What is your percent error, what are possible source of error? Be specific!

3. Does demonstrating a law with a simulation prove that it is true? Explain.

Part 2 - Lab

Materials:

• Low friction cart
• meter stick
• stopwatch
• small weights                
• pulley*

*A pulley will make the lab go smoother, but you might be able to get it to work without it.

Procedure

1. Mass your cart.
2. Tape off a meter across the top of a lab bench.
3. Attach a pulley to one side of the table so a hanging weight will pull the cart along the tape.
4. Attach your smallest weight to the cart.
5. Release the cart and time how long it takes for it to move on meter.
6. Repeat step 4 with four more hanging weight combinations.

Data

Cart Mass(kg):

Analysis

1. Calculate the acceleration of the cart for each scenario:

a = 2 d / t2

2. Plot a graph of Force versus Acceleration.

3. Find the slope of the best fit line through your graph.

Conclusion and Evaluation

1. Does the cart follow Newton’s Second Law? How do you know?

2. What is your percent error, what are possible source of error? Be specific!

3. Is the net force on the cart equal solely to the hanging weight? What other forces are present in the system and should technically be taken into account for this lab.

4. Use the given equations to derive the equation that was given to you - a = 2 d / t2.

Given:                 d = ½ (vi + vf) t         or         d = vavgt

                a = (vf - vi) / t