Newton's 3rd law?

Question

newton's 3rd law of motions states that there is an equal and opposite reaction to every action.
Which is not an illustration of this law?
1. a rifle recoils after firing
2. a duck pushes water backwards in order to move forward.
3. a pendulum bob swings first forward, then backwards.
4. when a boy jumps forward off a stationary skateboard, the skateboard goes backward.

Answer 1

number 3

Answer 2

2

Answer 3

Number 3. is not a simple 3rd law illustration. A swinging pendulum converts potential energy (height) to kinetic energy (velocity) back and force. In doing so the weight of the pendulum is resisted by an equal and opposite force at its pivot that constantly changes with height and velocity. When you are on a swing, you are 'weightless' on the swing seat at the top of the movement where motion reverses.

Answer 4

Number 3 in simple terms.

This is Simple Harmonic Motion under the influence of the Earth's gravitational force; as someone rightly said to be Newton's 3rd law the opposite reaction would be the response of the air particles it hits during it's swing.

Answer 5

answer 3

the opposite reaction of the swinging pendulum would be the pushing of the air.

EDIT:


I just had to come back and say some thing about this moron who answered after me.

Of course they all are, newtons laws govern motion.

However the description of number 3 does not explain the correct opposite reaction, therefore it is number 3

Answer 6

3. a pendulum bob swings first forward, then backwards.

Answer 7

No. 3, its Newtons 2nd law

Answer 8

They all are. Even a pendulum experiences forces opposing its motion, otherwise it would always continue in one direction.

Answer 9

the 3rd option, the pendulum bob moves due to centripetal acceleration

Answer 10

3...