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Newton’s 3 rd Law

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Newton’s 3rd Law

Physical Science Section 3.3

- Newton’s third law of motion
- when 1 object exerts a force on a 2nd object, the 2nd object exerts a force that is equal in size and opposite in direction to the force from the 1st object
- For every action, there is an equal & opposite reaction

- Swimming- swimmer exerts force on water; water exerts force on swimmer
- Action-reaction pairs act on different object

- Rocket engine- rocket engine exerts force on the hot gases produced by the fuel
- gases exert a force on the rocket and push it forward

- Orbit of earth in space influenced by:
- gravitational forces between the Sun and the Earth and between other planets and the Earth

- Discovery of Neptune
- Orbit of Uranus could not be explained by the planets known at the time

- Bicycle’s easier to stop than a car- less mass
- Less mass = less inertia and less momentum

- Object with less speed = less momentum
- Less speed = easier to stop

- Momentum- product of mass and velocity- influences how easily an object can be stopped
- P = m x v
- P : momentum Units kg*m/s2
- Has direction because velocity has direction
- Indicate direction of momentum

- Force can be calculated by using the final and initial momentum when an object changes its velocity.
- F = (mvf – mvi)/t)

- Law of conservation of momentum- total momentum does not change in a collision
- Momentum before collision = momentum after collision

- 2 objects collide when moving in the same direction
- first object slows and the second speeds up in the same direction

- 2 objects collide when moving in opposite directions with the same momentum
- Start with 0 momentum, collide, bounce off in opposite directions, still have 0 momentum