Download If the forces are equal in magnitude and opposite

Force Pairs Date ________
Forces always exist in pairs.
Force of the stake on the __________
A hammer exerts a force on the stake.
There must be a force to stop the hammer.
The stake exerts a force on the hammer.
When one object exerts a force on a second object, the second object exerts a force equal in magnitude and opposite in direction
on the first object.
Force of the hammer on the __________
If the forces are equal in magnitude and opposite in direction, why don't the forces cancel each other out?
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The two forces are acting on __________
___________________ _____________.
Forces cancel each other when they are
equal in magnitude and opposite in
direction acting on the SAME object.
When two forces are equal in magnitude
and opposite in direction and acting
on DIFFERENT objects they do not cancel out. They make objects move!!
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When two forces interact with one another
the forces that the objects exert on each
other are called an action­reaction pair.
The force object 1 exerts on object 2 is the action force. The force object 2 exerts on object 1 is the reaction force.
It does matter which is which since the action force and reaction forces occur AT THE SAME TIME.
The action ­ reaction forces are equal in magnitude and opposite in direction, but either object may still have a ________ _______________ acting on it
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Force pairs also apply to field forces (gravitational force, electrical force, magnetic force)
The gravitational force of the Earth pulls the rock downward and the gravitational force of the rock
pulls the Earth upward with a force of the same
magnitude.
The mass of the Earth is much greater than the mass
of the rock. The acceleration of the Earth is negligible but the rock does accelerate. 4
When a rifle is fired, the force exerted on the bullet has the same magnitude as the force
exerted on the rifle.
The same force on different objects produce different accelerations.
Bullet: force = acceleration
small mass
Rifle: force = acceleration
large mass
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A rocket accelerates because as the rocket throws out burned
rocket fuel at high velocity, the fuel exerts a force against
the rocket.
Why is a rocket easier to accelerate as it travels
in space away from the Earth?
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Arnold Strongman and Suzie Small pull on opposite ends of a rope in a tug of war.
The greatest force exerted on the rope is by
a) Arnold
b) Suzie
c)... both the same
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Two 100 N weights are attached to a spring scale as
shown.
What does the spring scale read?
Would the spring scale reading change
if the left pulley was removed and the
left side of the string was attached to a
stationary vertical pole?
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Suppose two carts, one twice as massive as the other fly apart when the compressed spring
that joins them is released.
1) How does the force exerted by the spring on the 1m ­ cart compare to the force exerted by the spring on the 2m ­ cart?
2) How fast does the 2m ­ cart roll compared to the smaller 1m ­ cart?
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Sprinting near the end of a race, a runner with a mass
of 60 kg accelerates from 6.0 m/s to 7.0 m/s in 2 seconds.
1) What is the runner's average acceleration?
2) To gain speed the runner produces a backward force
on the ground. What is this force?
3) What is the force that the ground exerts on the runner?
4) Why don't these two forces cancel out?
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