Download Unit 2 Lesson 3

Unit 2 Lesson 3 Forces
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Unit 2 Lesson 3 Forces
Force of Nature
What is a force?
• In science, a force is a push or a pull.
• All forces are vectors.
• The unit that measures force is the newton (N).
• Forces do not always cause motion.
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Unit 2 Lesson 3 Forces
How can forces act?
• Forces can act on objects that are in contact or on
objects that are at a distance.
• Gravity is a force that pulls objects toward Earth.
• Magnetic forces can act at a distance or by
contact.
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Unit 2 Lesson 3 Forces
How can forces act?
• Forces can transfer energy from one object to
another.
• Forces change an object’s motion by accelerating
it unless the forces are balanced.
• Friction is force that occurs between objects that
are touching.
• Friction causes objects to slow down.
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Unit 2 Lesson 3 Forces
In the Balance
How do multiple forces interact?
• The net force is the combination of all the forces
acting on an object.
• When forces act in the same direction, they are
added to determine net force.
• When forces act in opposite directions, the smaller
force is subtracted from the larger force.
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Unit 2 Lesson 3 Forces
How do multiple forces interact?
• A net force of zero means the forces are balanced
and will not cause a change in motion.
• Unbalanced forces produce a change in motion, or
acceleration.
• Acceleration is always in the direction of the net
force.
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Unit 2 Lesson 3 Forces
How do multiple forces interact?
• Unbalanced forces are not always opposite.
• Net force will be in a direction that is a
combination of the individual forces.
• When forces are not of equal strength, the
direction will be closer to the direction of the
stronger force.
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Unit 2 Lesson 3 Forces
How do multiple forces interact?
• What would happen to the girl’s direction if the
dog at the bottom of the picture was very small?
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Unit 2 Lesson 3 Forces
Hitting the Brakes
How do forces act on objects?
• Sir Isaac Newton described three laws of motion
that explain the relationship between force and
motion.
• Newton’s first law is that an object at rest remains
at rest, and an object in motion maintains its
velocity, unless it experiences an unbalanced
force.
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Unit 2 Lesson 3 Forces
How do forces act on objects?
• An object will not start moving unless a push or
pull acts on it.
• Objects in motion will continue to move unless a
push or pull changes that motion.
• Newton’s first law is also called the law of inertia.
• Inertia is the tendency of all objects to resist any
change in motion.
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Unit 2 Lesson 3 Forces
How do forces act on objects?
• Newton’s second Law is that the acceleration of an
object depends on the mass of the object and the
amount of force applied.
• force = mass × acceleration (F = ma)
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Unit 2 Lesson 3 Forces
A Matching Pair
How do force pairs act?
• Newton’s third law is that whenever one object
exerts a force on a second object, the second
object exerts an equal and opposite force on the
first.
• In other words, all forces act in pairs.
• Action and reaction forces are present even when
there is no motion.
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Unit 2 Lesson 3 Forces
How do force pairs act?
• Action and reaction forces in a pair do not act on
the same object.
• The effects of action and reaction forces often are
different.
• Multiple forces can act on an object at once.
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