Physics 1

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page 1

Momentum �⃗⃗� = 𝒎�⃗⃗� http://ophysics.com/e2.html We are going to examine the way what happens during collisions. This program uses Elasticity to govern how elastic (energy conserving) the collision is, with e=1 being elastic, e=0 being completely inelastic, and between being inelastic. e is simply the square root of

the percentage of energy conserved, so 𝑒 = √ 𝐾𝐸𝑓

𝐾𝐸𝑖 .

Set the masses to equal and the velocity to of one block to 0. Set elasticity to 0. What do you expect to happen? What happens? Try changing the masses. What do you observe? Pause the simulation after the collision so you can read off the values. Does it act as you expect? Try changing the initial velocities. Be sure to try with both masses going in the same direction initially (but make sure they actually collide). Also try equal and opposite velocities. How is the motion effected?

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page 2

Reset the simulation to the even masses and one to 0 initial velocity, but set elasticity to 1. This creates a perfectly elastic collision. The equations for elastic collisions are complicated to derive. You can look these up if you need them.

𝑣𝑓1 = 𝑣𝑖1 𝑚1−𝑚2

𝑚1+𝑚2 + 𝑣𝑖2

2𝑚2

𝑚1+𝑚2 𝑣𝑓2 = 𝑣𝑖1

2𝑚2

𝑚1+𝑚2 + 𝑣𝑖2

𝑚2−𝑚1

𝑚1+𝑚2

Using these equations, what do you expect to happen? Try giving them differing initial velocities. Pause the simulation after the collision so you can read off the values. Be sure to try with both masses going in the same direction initially (but make sure they actually collide). Also try equal and opposite velocities. Does it act as you expect? Try making the blocks unequal mass. What do you expect to happen? If you try it in the simulation, what do you see? Try different combinations of velocities.

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page 3

Reset the simulation to the default values, but set elasticity to 0.5. This creates an inelastic collision, the most general type. For inelastic collisions, we cannot find both speeds after the collision, we can only find one speed after the collision once we know the other. Try several combinations of initial velocities and masses, and comment on what you see. Be sure to try with both masses going in the same direction initially (but make sure they actually collide). Although we cannot get an exact equation, you should be able to see some patterns.