Virtual Collisions (PhET)

As you embark on this exercise, please keep in mind the following points:

• The equation for momentum (p) is: p = mass * velocity (p = m*v)
• Momentum is a VECTOR. That means you have to keep track of direction (represented by negative or positive values). Positive values for velocity and momentum indicate the direction is to the right. Negative values for velocity and momentum indicate the direction is to the left.
• Before Momentumis the momentum given in the table before the simulation is played. After Momentumis the momentum given in the table after the objects have collided.
• Ignore the Position data.

Go to the following website: https://phet.colorado.edu/sims/html/collision-lab/latest/collision-lab_all.html.

Click Intro.

Set up the following:

• Make sure that Elasticity is set at 100%
• On the bottom, select More Data. This table provides mass, velocity, and momentum values.

Experiment 1 (ELASTIC collisions):

1. Input the initial Trial 1 settings for mass and velocity as indicated in Table 1. Record the before momentum of mass 1 and before momentum of mass 2given in the simulation data table.
2. Play the simulation. Once the objects collide, pause the simulation. Record the after velocity and after momentum for each object in Table 1. Reset the simulation.
3. Add the two before momentums and the two after momentums. Record the sums in Table 2.
4. Complete steps 1-3 for the mass and velocity setting represented for Trial 2-4 in Table 1. Record the data in Table 1 and the momentum totals for each trial in Table 2.

	Mass 1 (kg)	Before Velocity of Mass 1 (m/s)	Before Momentum of Mass 1 (kg m/s)	Mass 2 (kg)	Before velocity of Mass 2 (m/s)	Before Momentum of Mass 2 (kg m/s)	After Velocity of Mass 1 (m/s)	After Momentum of Mass 1 (kg m/s)	After Velocity of Mass 2 (m/s)	After Momentum of Mass 2 (kg m/s)
Trial 1	0.5	1.0		1.5	0
Trial 2	3.0	1.0		1.0	-3.0
Trial 3	2.0	2.0		2.0	-2.0
Trial 4	1.0	3.0		1.0	1.0

Table 1:Experiment 1 settings and results

	Total before momentum (kg m/s)	Total after momentum (kg m/s)
Trial 1
Trial 2
Trial 3
Trial 4

Table 2:Total before and after momentums

Experiment 2 (INELASTIC collisions):

1. Shift the elasticity bar to ANY NON-ZERO NUMBER between 0 and 100%.
2. You have full choice as to your masses and before velocities.
3. Add the before momentums together to find the total before momentum (p).
4. After playing each trial, record the after velocities and the after momentum for each object.
5. Add the after momentums together to find the total after momentum (p).

Complete steps 1-5 for trials 1 and 2. Be sure to include some change (i.e., change one mass, both masses, and/or before velocities) for each trial. Also, be sure to choose a different NON-ZERO number for elasticity for Trial 2. The elasticity for Trial 3 should be zero.

TRIAL 1: Elasticity = __________

Before Collision

Mass of object 1 = __________ before v of 1= __________ before p of 1 = __________

Mass of object 2 = __________ before v of 2 = __________ before p of 2 =__________

Total before p = __________

START COLLISION

After Collision

Mass of object 1 = __________ after v of 1= __________ after p of 1 = __________

Mass of object 2 = __________ after v of 2 = __________ after p of 2 =__________

Total after p =__________

TRIAL 2: Pick a new non-zero, non-100% elasticity and run again. Elasticity = __________

Before Collision

Mass of object 1 = __________ before v of 1= __________ before p of 1 = __________

Mass of object 2 = __________ before v of 2 = __________ before p of 2 =__________

Total before p = __________

START COLLISION

After Collision

Mass of object 1 = __________ after v of 1= __________ after p of 1 = __________

Mass of object 2 = __________ after v of 2 = __________ after p of 2 =__________

Total after p =__________

TRIAL 3: Set Elasticity to exactly 0%

Before Collision

Mass of object 1 = __________ before v of 1= __________ before p of 1 = __________

Mass of object 2 = __________ before v of 2 = __________ before p of 2 =__________

Total before p = __________

START COLLISION

After Collision

Mass of object 1 = __________ after v of 1= __________ after p of 1 = __________

Mass of object 2 = __________ after v of 2 = __________ after p of 2 =__________

Total after p =__________

Questions:

1. The collisions in Experiment 1 were ELASTIC while those in Experiment 2 were (somewhat) INELASTIC (Trial 3 of Experiment 2 was completely inelastic). In your own words, what is the difference? (Hint: Try running the simulation 2 different times, back-to-back, with the same input values. The first trial should have elasticity set at 100%; the second trial should have elasticity set at 0%. This is a qualitative observation, meaning you should focus on visual observations about the differences between the 2 collisions rather than on any quantitative data.)
2. Did the mass of either object ever change as a result of the collisions? Explain why or why not.

3. Did the velocity of either object ever change as a result of the collisions? Explain why or why not.

4. Study the values of Total Before Momentum with those of Total After Momentum for each collision in both experiments. Did the total momentum ever change? Explain why or why not.