Every action has an equal and opposite reaction.
Newton’s Third Law explains that forces exist in equal and opposite pairs. If a force acts on an object in one direction then an equal forces pushes back in the opposite direction.
We have adapted our catapults so that they sit on plastic rollers. This reduces the friction between the board and the table. We used oversized projectiles (50 g balls of plasticine) and measured how much recoil there was when we fired the catapults.
Smaller masses tended to produce less recoil. If the catapult was fired with no projectile the recoil was usually less than 1 cm.
Table of Results for the Recoil of the Catapult Firing Three Different Masses.
50 g
(cm)
53
49
37
46
51
10 g
(cm)
31
27
22
30
25
0 g
(cm)
0
1
1
0
1
Questions…
- What is Newton’s First law?
- When was Newton born?
- When you wax your skis, which force are you trying to reduce?
- What was the ‘mean’ recoil distance when firing the 50 g, 10 g and 0 g catapult?
- Why do you think that the recoil was greater firing the 50 g projectile than the 10 g projectile?
- From the video it looks like the recoil would have been greater if the catapult had not fallen off the rollers. How could we modify our design to see the complete recoil produced when the catapult is fired?
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