Physical Interactions between Particles: Newton’s Laws of Motion Investigation
Part I: Interactions between particles of similar mass.
Materials: Two marbles of similar (close to the same) mass, a ruler with a center groove, a balance for
measuring mass, and if your instructor permits a stopwatch.
General Directions: Using your index finger, make one marble move in a straight line along the center
groove of the ruler with a speed between 10 – 15 cm/s. Practice your technique until you can reproduce
this speed fairly consistently. Next place the other marble on center of the ruler. (See image below.)
Finally using your technique, make one marble collide with the other stationary marble in the middle. Do
as many repeat trials as necessary while answering the questions below. For each trial you should try to
reproduce about the same speed for the marble prior to the collision. Finally construct a data table similar
to the one below to record your observations.
Speed Before Collision
Observations with
colliding speeds:
1 (medium speed)
2 (faster speed)
3 (½medium speed)
Marble 1
(inertia: ________g
Marble 1
(inertia: _______g
Speed After Collision
Marble 1
(inertia: _______g
Marble 1
(inertia: _______g
1. What is the approximate speed (in centimeters/second) of
the moving marble prior to the collision with the second?
2. What is the approximate speed (again in cm/s) of this marble
after the collision?
3. What is the speed of the stationary marble prior to the
collision?
4. What is the speed of the (initially) stationary marble after the
collision?
5. How does the speed of the initially moving marble compare with the speed of the stationary
marble (after the collision)?
6. How would you describe the motion of the two-marble system before and after the collision?
7. What do you think causes the change in motion of each marble?
8. Repeat steps 1 – 6 using a consistent speed that is greater than the previous speed of the first
marble.
9. Repeat steps 1 – 6 using a consistent speed that is less than (~ ½) the first one.
o Discuss with your group your results, summarize your data, and have your
instructor check your results and initial.
Investigation Part II: Effects of Inertia on Motion – subplot A
Construct a data table as in Part I. Obtain two marbles of distinctly different masses. Make the less massive
marble to move in a straight line and collide with the other (more massive) stationary marble.
1. What is the speed of the (less massive) marble prior to the collision with the more massive marble?
2. What is the speed of this marble after the collision?
3. What is the speed of the stationary (more massive) marble prior to the collision?
4. What is the speed of the (more massive) marble after the collision?
5. How does the speed of the initially moving (less massive) marble compare with the speed of the
stationary (more massive) marble (after the collision)?
6. How would you describe the motion of the two-marble system before and after the collision? HINT:
Think not only about the velocities, but also about the masses of the marbles.
7. How do the forces acting on each marble compare? Is one larger than the other? Before answering
remember that the marbles have different masses. Explain.

Discuss with your group your results, summarize your data, and have your
instructor check your results and initial.
Investigation Part III: Effects of Inertia on Motion – subplot A
Construct a data table as in Part I. Obtain two marbles of distinctly different masses Finally, rearrange the
last situation by having the more massive marble collide with the less massive marble.
1. What is the speed of the (more massive) marble prior to the collision with the less massive marble?
2. What is the speed of this marble after the collision?
3. What is the speed of the stationary (less massive) marble prior to the collision?
4. What is the speed of the (less massive) marble after the collision?
5. How does the speed of the initially moving (more massive) marble compare with the speed of the
stationary (less massive) marble (after the collision)?
6. How would you describe the motion of the two-marble system before and after the collision? HINT:
Think not only about the velocities, but also about the masses of the marbles.
7. How do the forces acting on each marble compare? Is one larger than the other? Before answering
remember that the marbles have different masses. Explain.

Discuss with your group your results, summarize your data, and have your
instructor check your results and initial.
TEACHER NOTES
The product of the mass of an object and its velocity (or speed if in one direction) is the momentum
of the object. The mathematical equation for this relationship is: momentum = mass x velocity. In
symbols: p = mv . Sir Isaac Newton understood that the change in an object’s motion (and therefore
its momentum) was the result of some outside interaction acting on the object. This outside
interaction acting on an object is called a force. During a collision, the change in an object’s
momentum (motion) is directly proportional to the force acting on the object. This relationship is
part of what is known as Newton’s 2nd law of motion. Keep this in mind while conducting the
following investigations.