Transcript Newton’s 3rd Law

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
Newton’s 3rd Law
• 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 velocityinfluences how easily an object can be
stopped
–P=mxv
– 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