forces. what is a force? forces are described by their strength and direction
TRANSCRIPT
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Forces
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What is a force?• Forces are described by their strength and
direction.
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What is a force?
• Forces are a push or a pull.
• One object can exert a force on another
object.
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Units of Force
• The SI unit of force is the
newton (N), named for Issac
newton.
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Measuring Forces
30 N
• Arrows always point in the direction of the force. The longer the arrow…the
greater the force.
5 N
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Measuring Forces
7 N 7 N 14 N
8 N 5 N14 N
• Forces are added when they go in the same direction. They are subtracted when they go in opposite directions. The result
is a net force.
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Measuring Forces
7 N 7 N0 N
• In this case both forces cancel each other out because they are equal.
There is NO net force.
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Unbalanced Forces
• Unbalanced forces can cause an object to start moving, stop moving or change
direction.
• Unbalanced forces acting on an object result in a net force and cause a change in
the objects motion.
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Unbalanced Forces
• This net force causes the box to move to the right.
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Unbalanced Forces
• Two equal forces result in no net change – the box does not move.
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Unbalanced Forces
• Two equal forces result in no net change – the box does not move.
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Balanced Forces
• Equal forces acting on one object in opposite directions.
• They do not change the objects motion.
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Friction and Gravity
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Friction
• The force that two surfaces exert on each other when they rub against
each other is friction.
• There are a few types of friction.
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Friction
The strength of the force of friction depends on two factors:
• How hard the surfaces push together.• The type of surface involved.
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Friction and Surfaces
• Some things have a low coefficient of friction, like
ice. It is smoother the coefficient is low.
• If it is bumpy or rough there is a high coefficient
of friction.
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Types of Friction: Static Friction
• Static friction is a type of friction that acts on objects that are NOT moving.
• It takes extra force to move something that is not already moving.
• Must exert a force GREATER than the static friction.
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Types of Friction: Static Friction
It really takes a lot of force to get past the amount of static friction here!
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Types of Friction: Sliding Friction
• Sliding friction occurs when two solid surfaces slide over each other.
A ballet dancer will put powder on their slippers to prevent the sliding friction
from occurring.
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Types of Friction: Rolling Friction
• When an object rolls across a surface – rolling friction occurs.
A skateboarder is demonstrating rolling
friction…how?
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Types of Friction: Fluid Friction
• Fluid friction occurs when an object pushes a fluid.
A surfer’s board is helping them overcome the force of fluid
friction.
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Gravity
• Gravity is a force that pulls objects toward each other
It is also a force that can be
measured. On Earth Gravity is
different than on the moon.
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Factors affecting gravity
• Two factors that affect the
gravitation attraction between objects are MASS
and DISTANCE
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Gravity
The force of gravity acts between all objects
If mass increases, the force of gravity increases.
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Gravity
If distance increases, the force of gravity decreases.
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Mass VS Weight
• Mass is a measure of the amount of matter in an object.
• Weight is a measure of the gravitational force exerted on an object. Weight = Mass X Gravity
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Free Fall
• When the only force acting on an object is gravity, the object is
said to be in free fall.
• In free fall, the force of gravity is an
unbalanced force. This causes an object
to accelerate.
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Acceleration Due to Gravity
• Near the surface of Earth – acceleration due to gravity is 9.8
m/s
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Acceleration Due to Gravity
• All objects in free fall accelerate at the same rate regardless of their masses.
• These rocks and this feather would fall at the same rate!
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Air Resistance
• Air resistance creates a type of fluid friction
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Air Resistance
• Air resistance increases with more surface area.
• Air resistance increases with increasing velocity.
• The greatest velocity a falling object reaches is called its terminal velocity. This is reached when the force of air resistance equals the weight of
the object.
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Projectile Motion
An object thrown is called a projectile.
The force of gravity will act on the projectile.
At first it goes upward, but eventually gravity pulls it back to the ground.
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Projectile Motion