This activity allows you to observe momentum conservation for a collision between a big fish and a little fish. Before the collision (a.k.a. lunch), the little fish is in motion and the big fish is at rest. After the collision, the two fish move together at the same speed. One can reason proportionally to predict the post-collision speed.
Fish Catch
Begin Activity
20 g
80 g
15 g
75 g
25 g
You may view and analyze nine different situations. The situations differ in terms of the relative mass of the two fish. Click on an icon to see the animation and accompanying analysis.
60 g
45 g
125 g
100 g
60
A little fish with a mass of 20 grams and a velocity of 80 cm/s is eaten by a big fish that has a mass of 100 grams and is initially at rest. The two fish move with the same speed after the collision (i.e., after lunch).
20
0.0
1600
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80.0
Repeat Animation
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Before lunch, only the little fish has momentum. The before-lunch momentum is the result of 20 grams in motion. After lunch, the big fish and little fish move with the same velocity. A total of 80 grams is in motion. The amount of mass in motion has increased by a factor of 4. For total momentum to be conserved, the velocity with which this mass moves decreases by a factor of 4 - from 80.0 cm/s to 20.0 cm/s.
1200
900
45
20.0
A little fish with a mass of 15 grams and a velocity of 80 cm/s is eaten by a big fish that has a mass of 45 grams and is initially at rest. The two fish move with the same speed after the collision (i.e., after lunch).
Analyze the before- and after-lunch velocity and momentum values of the big fish, the little fish, and the total (or system). What pattern do you observe?
15
300
16.0
960
Analyze the before- and after-lunch velocity and momentum values of the big fish, the little fish, and the total (or system). What pattern do you observe?
240
A little fish with a mass of 15 grams and a velocity of 80 cm/s is eaten by a big fish that has a mass of 60 grams and is initially at rest. The two fish move with the same speed after the collision (i.e., after lunch).
13.3
1000
A little fish with a mass of 15 grams and a velocity of 80 cm/s is eaten by a big fish that has a mass of 75 grams and is initially at rest. The two fish move with the same speed after the collision (i.e., after lunch).
75
200
A little fish with a mass of 20 grams and a velocity of 80 cm/s is eaten by a big fish that has a mass of 60 grams and is initially at rest. The two fish move with the same speed after the collision (i.e., after lunch).
400
80
320
A little fish with a mass of 20 grams and a velocity of 80 cm/s is eaten by a big fish that has a mass of 80 grams and is initially at rest. The two fish move with the same speed after the collision (i.e., after lunch).
1280
100
1333
267
2000
1500
500
A little fish with a mass of 25 grams and a velocity of 80 cm/s is eaten by a big fish that has a mass of 75 grams and is initially at rest. The two fish move with the same speed after the collision (i.e., after lunch).
25
A little fish with a mass of 25 grams and a velocity of 80 cm/s is eaten by a big fish that has a mass of 100 grams and is initially at rest. The two fish move with the same speed after the collision (i.e., after lunch).
125
A little fish with a mass of 25 grams and a velocity of 80 cm/s is eaten by a big fish that has a mass of 125 grams and is initially at rest. The two fish move with the same speed after the collision (i.e., after lunch).
1667
333