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Physics 20: Dynamics

eMATH Activity

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Testing Newton's Second Law

The Question:

Is Newton's second law valid?

The Hypothesis:

The acceleration of an object is directly proportional to the net force applied and inversely proportional to the mass.

Testing the Hypothesis:

Using provided force, mass, and acceleration data of an object being pulled on a smooth surface, work out the ratio of net force divided by the mass. Then use a graphing calculator to plot the points on a graph of acceleration against this ratio. Next, use the graphing calculator to identify the function that best models the data and plot the line graph of the function.

The Data:

Acceleration
(m/s2)
[forward]
Force
(N)
(pulls)
Mass
(m)
(kilograms)
1.0 7.5 5.0
2.0 12 4.0
4.0 18 3.0
4.5 47 7.0
5.0 11 1.5
6.0 16 1.8
8.0 54 4.5
10 45 3.0

Write the Equation:

1. What physical quantities do x and y represent?
2. Write the equation that best models the relationship between acceleration and the ratio of net force divided by the mass.
3. What is the proportionality constant? What property of the graph does it represent?
4. To what extent do the data support Newton's second law?
5. a) Why was the proportionality constant not equal to one as it is in Newton's second law equation?

b) What are the units of the proportionality constant?
6. Why was the y-intercept so close to zero?
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