LAB: F = ma
Name_____________________________
Background: Newton’s 2nd Law can be summed up by the equation F = ma. For a
constant force, the mass and acceleration are inversely proportional to one another. In
this lab, we will first use a constant force with carts of 3 different masses. In part B, the
force will change while the mass stays the same.
Procedure: Obtain a piece of string roughly 2 m in length. Tie one end to the cart and
the other end to the mass. The mass should be hanging over the edge of the table, but at
least 75 cm above the floor. At the same instant the mass is dropped, start the timer.
Record the time required for the cart to travel 0.75 m. Do three trials and calculate the
average.
Data: Part I (doubling the force)
Mass of
Mass of
Time 1 (s)
falling
cart (kg)
weight
(kg)
Time 2 (s)
Time 3 (s)
Avg. Time
(s)
Distance
(m)
0.100
2.44
0.75
0.200
2.44
0.75
We can calculate the acceleration for an object starting at rest using “a = 2x / t2“.
Acceleration with 0.100 kg mass
__________ m/s2
Acceleration with 0.200 kg mass
__________ m/s2
Data: Part II (changing the mass)
Mass of
Mass of
Time 1 (s)
falling
cart (kg)
weight
(kg)
Time 2 (s)
Time 3 (s)
Avg. Time
(s)
Distance
(m)
0.100
1.44
0.75
0.100
2.44
0.75
0.100
3.44
0.75
Acceleration with 1.44 kg cart
__________ m/s2
Acceleration with 2.44 kg cart
__________ m/s2
Acceleration with 3.44 kg cart
__________ m/s2
Lab: F=ma follow up questions
1. Determine the amount of force being applied to the cart in each trial using
Newton’s 2nd Law (F = ma).
2. The motion of the cart could best be described as having a (constant, changing)
velocity and a (constant, changing) acceleration?
3. How did the mass of the cart and its contents affect the acceleration of the cart?
Explain.
4. How did the amount of force applied to the cart (by the falling weight) affect the
acceleration when the mass of the cart was unchanged? Explain.
5. Could we use the mass of the falling weight times 9.80 to determine the force
applied to the cart (Hint: Draw a free body diagram for the falling weight.)? Try it
for one of your trials and compare it to the mass x acceleration calculated above in
question #1.