what is force? - pc\|macimages.pcmac.org/sisfiles/schools/ms/desotocounty/hornlakemiddle… ·...
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What is force?
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Net force
• Net force: combination of all the forces
acting on an object
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Net force
• If two forces are in opposite directions, then the net force is the difference.
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Net force
• If two forces are in the same direction, they add together to get the net force.
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Balanced force
Balanced Force: if two equal forces are being exerted on an object in opposite directions.
This will result in a net force of zero.
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Balanced force
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Unbalanced force
The effects don’t cancel each other. The objects net force is NOT zero.
The object moves.
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Unbalanced force
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Example
A 10-newton force and a 15-newton force are acting from a single point in opposite
directions. What additional force must be added to produce equilibrium?
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Newton’s 1st law
• An object at rest tends to stay at rest,
and an object in motion tends to stay
in motion, with the same direction and
speed.
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Friction
• Friction: a force that acts against the
motion between two objects; this slows
an object down
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Static friction
Static friction is the attraction between
the atoms on the two surfaces that are in
contact.
This causes the surfaces to stick together.
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Sliding friction
While static friction keeps an object at
rest, sliding friction slows down an
object that slides.
A result of the microscopic roughness of
two surfaces.
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What do you think?
What is the difference
between static friction and
sliding friction?
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Rolling friction
Needed to make a wheel or tire turn.
Occurs between the ground and the part of the tire touching the ground.
Keeps the tire from slipping on the ground.
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Newton’s 2nd Law
An object acted upon by a force will
accelerate in the direction of the force.
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Newton’s 2nd Law
Net Force = mass x acceleration
Force is measured in newtons (N)
Fnet
m a
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Acceleration
• The second law tells how to calculate the acceleration of an object if its mass and the forces acting on it are known.
Acceleration =
Net Force Mass
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example
Using what we know lets say that on the way to work my vehicle breaks down. The car weighs 1000 Kg. As I am pushing the car I am able to make it roll
at 0.05 m/s². How much force am I applying?
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Example
A car with a mass of 1,500 kg has an acceleration of 3 m/s². Find the force
acting on the car.
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You pull a 10 kg sled so that the net force on the sled is 5 N. What is the acceleration?
Example
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example
You throw a baseball with a mass of 0.15 kg so it has an acceleration of 40 m/s². Find the force
you exerted on the baseball.
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example
A human cannonball with a mass of 80 kg is fired out of a cannon with a force of 2,400 N.
Find the acceleration.
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Gravity vs. Weight
Gravity: an attractive force that pulls objects toward each other.
Depends on the mass of the objects and distance between them.
Becomes weaker the farther apart the objects are.
Decreases as the mass of the objects decrease.
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Gravity vs. Weight
The force of gravity causes all objects near Earth’s surface to fall with an acceleration of 9.8 m/s².
Gravitational Force:
F = m x (9.8 m/s²)
This gravitational force is also called weight.
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Gravity vs. Weight
Weight: the gravitational force between you and Earth.
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Newton’s 3rd law
Newton’s 3rd Law: for every force there is an equal and opposite force.
Ex. if you push on a wall, it will push back on you as hard as you are pushing on it.
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Balloon Rocket lab
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Paddling a Canoe
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Rocket Launch
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Jumping Into Pool