PY12U Lab - Conservation of Momentum

Purpose: To observe the law of conservation of momentum during one dimensional interactions: elastic collisions, inelastic collisions and explosions.

Hypothesis: The heat loss/gain during an ...

A) elastic collision will be negligible Q <= 5% of Ki.

B) inelastic collision will be significant Q >= 20% of Ki.

C) explosive interaction will be significant Q << 0 J.

Procedure

• In class use the dynamics carts which mass around 1 kg with some brass masses. Some carts have a spring for elastic and explosive interactions. Some carts have Velcro for inelastic interactions. Mass the carts to find the exact masses for more accurate lab results.
• If at home then use the Physics Classroom simulator (https://www.physicsclassroom.com/Physics-Interactives/Momentum-and-Collisions/Collision-Carts/Collision-Carts-Interactive ).
• If in class or at home conduct two of each interaction mentioned above in the hypothesis. For each interaction do so once with two carts of equal mass (ex. approximately 1 kg with 1 kg or 2 kg with 2 kg - you pick), then once with one cart more massive than the other by 1 to 3 kg (ex. 1 kg with 4 kg or 5 kg with 6 kg - you pick).

Interaction Type	Equal Masses	Unequal Masses
Elastic	E1	E2
Inelastic	I1	I2
Explosive	X1	X2

Fill in the observation chart and then provide sample calculations for either *E2 or *I2. You may find it impossible to calculate %Q for explosive interactions.

Sample Observations Chart

Interaction	m1 (kg)	m2 (kg)	v1 (m/s)	v2 (m/s)	v1/ (m/s)	v2/ (m/s)	P (Ns)	P/ (Ns)	K (J)	K/ (J)	% P	Q (J)	% Q vs K
E1	1	1	5	-5	-5	5	0	0	25	25.0	0	0.0	0
*E2	1	2	5	-8	-12.3	0.7	-11	-10.9	76.5	76.1	0.91	0.4	0.52
I1	2	2	5	-8	-1.5	-1.5	-6	-6	89	4.5	0	84.5	94.94
*I2	1	2	5	-3	-0.3	-0.3	-1	-0.9	21.5	0.1	10	21.4	99.53
X1	1	1	0	0	-10	10	0	0	0	100.0	0	-100.0	n/a
X2	1	3	2	2	-8	5.3	8	7.9	8	74.1	1.25	-66.1	n/a

Synthesis Questions

1. In some collisions/interactions, the total momentum was zero before, during and after the collision/interaction, yet the total kinetic energy did not remain constant. Use this observation to explain why it is important to distinguish between scalar and vector quantities when analyzing conservation of momentum and conservation of energy.
2. How could the results of this investigation be applied to determine the mass of a sealed refuse bag on board the International Space Station. (The ISS is in constant free fall around the Earth). To really explain your answer, draw a diagram, include some sample numbers ex. room is 8 m long, astronaut has a known mass of 60 kg, stopwatch times of ... and show how you would calculate the mass of the refuse (garbage) bag.
3. If we added adjustable friction pads to the carts how would this have affected the results of the investigation? Imagine small little brakes adding a few Newtons of friction force before, during and after the collision/interaction.

Conclusion:

• Write one based on the results and hypotheses.