unit 15 lesson 1 what are forces? · 3/15/2018 · lesson 1 what are forces? ... the oars, causing...
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Unit 15 Lesson 1 What Are Forces?
Pushing and Pulling
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• A force is a push or pull.
• Forces can cause an
object at rest to move, speed up, slow down, change direction, or stop.
• Forces can change the
shape of an object.
Unit 15 Lesson 1 What Are Forces?
Pushing and Pulling
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• For example, when rowers pull back on oars, the oars push against the water. The water pushes back against the oars, causing the boat to move.
• The larger the force, the greater the change it can cause to the motion of an object. Smaller forces cause smaller changes.
Unit 15 Lesson 1 What Are Forces?
Pushing and Pulling
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 15 Lesson 1 What Are Forces?
Pushing and Pulling
Copyright © Houghton Mifflin Harcourt Publishing Company
• Spring scales are used to measure force in units called Newton (N).
Unit 15 Lesson 1 What Are Forces?
Pushing and Pulling
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Two Common Forces
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Gravity
• Gravity is a force of attraction toward the center of Earth. It acts even when objects are not touching.
Unit 15 Lesson 1 What Are Forces?
Two Common Forces
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Gravity
Unit 15 Lesson 1 What Are Forces?
Two Common Forces
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Gravity
• The size of the force
increases as the mass of the objects increases.
Unit 15 Lesson 1 What Are Forces?
Two Common Forces
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Gravity
Unit 15 Lesson 1 What Are Forces?
Two Common Forces
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Gravity
• The size of the force
decreases as the distance between the objects increases.
Unit 15 Lesson 1 What Are Forces?
Friction
• Friction is a force that opposes motion and acts between two objects that are touching.
• Friction can also exist between
air and a moving object. This is called air resistance.
• Friction can also change the energy of motion into thermal energy.
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Unit 15 Lesson 1 What Are Forces?
Unit 15 Lesson 1 What Are Forces?
Balanced or Unbalanced?
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• Balanced forces are forces on an object that are equal in size and opposite in direction.
• Unbalanced forces are
forces that cause a change in motion.
• A force must overcome the
force of friction before an object will move.
Unit 15 Lesson 1 What Are Forces?
Balanced or Unbalanced?
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Unit 15 Lesson 1 What Are Forces?
Balanced or Unbalanced?
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Unit 15 Lesson 1 What Are Forces?
Balanced or Unbalanced?
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Unit 15 Lesson 1 What Are Forces?
Pull (or Push) Harder!
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Unit 15 Lesson 1 What Are Forces?
Pull (or Push) Harder!
Copyright © Houghton Mifflin Harcourt Publishing Company
• A large force will cause a large change in the motion of an object. A small force will cause little change.
• The large force makes the object change its velocity, or accelerate, quickly.
• Changes in velocity include changes in
speed and changes in direction.
Unit 15 Lesson 1 What Are Forces?
I’m Not Moving!
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• The larger the force applied to an object, the greater the acceleration.
Unit 15 Lesson 1 What Are Forces?
Pull (or Push) Harder!
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• What should the boy do differently to make the bell ring?
Unit 15 Lesson 1 What Are Forces?
I’m Not Moving!
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• When the same force is applied, objects with greater mass accelerate more slowly than objects with less mass.
Unit 15 Lesson 1 What Are Forces?
I’m Not Moving!
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• The less an object’s
mass is, the less force is needed to change its motion.
Unit 15 Lesson 1 What Are Forces?
I’m Not Moving!
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Unit 15 Lesson 1 What Are Forces?
I’m Not Moving!
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• Why does it take the full truck longer to stop than the empty truck?
Unit 15 Lesson 1 What Are Forces?
Let’s Go to Mars!
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• An understanding of forces helped to safely send a spacecraft to Mars.
Unit 15 Lesson 1 What Are Forces?
Let’s Go to Mars!
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• Balanced forces allowed a
spacecraft to move in one direction at a constant velocity through space.
• Once the spacecraft reached
Mars, it accelerated toward the surface because of gravity.
Unit 15 Lesson 1 What Are Forces?
Let’s Go to Mars!
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Unit 15 Lesson 1 What Are Forces?
Let’s Go to Mars!
Copyright © Houghton Mifflin Harcourt Publishing Company