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Chapter 13 Lessons

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Transcript

  • 1. Chapter 13 Forces in Motion
  • 2. You Will Discover:
    • How motion is measured.
    • How force affect motion, work, power.
    • What Newton’s laws of motion are.
    • How simple machines make work easier.
  • 3. Chapter 13 Vocabulary
    • Velocity: the speed and direction of an object’s motion
    • Force: a push or pull that acts on an object
    • Work: energy used when a force moves on an object
    • Power: the rate at which work is done
    • Equilibrium : the state in which the net force is zero
    • Inertia: the tendency of an object to resist a change in motion
    • Acceleration: the rate at which the velocity of an object changes over time.
    • Machine: a device that changes the direction or the amount of effort needed to do work.
  • 4. Lesson 1: How can you describe motion?
    • Types of Motion
    • Steady or Constant - the Earth has steady motion as it moves around the Sun.
    • Variable - cars, trucks, and buses because they move in many directions and at many speeds.
    • Periodic - a pendulum, swings back and forth
    • Circular - wheels
    • Vibrational - a rubber band when you pluck it
  • 5. Examples of Motion Steady or Constant Periodic Variable Vibrational Circular
  • 6. Speed
    • Average Speed: describes how far an object moves during a certain amount of time.
    • Average Speed = Distance
    • Time
    • The motion of an object cannot be measured by just looking at the object.
    • Motion is always measured in relationship with some location called a point of reference.
    • The speed at which a person is moving can vary according to which point of reference you use.
  • 7. Speed Formula
    • Point of Distance Time Speed
    • Reference
    • Train Car 10 m 5 s 10m = 2 m/s 5 s
    • Signal 150 m 5 s 150m = 30 m/s
    • Light 5 s
  • 8. Velocity
    • Speed and Velocity are not the same!
    • Velocity describes the speed and the direction of an object’s motion.
    • Example: the speed of the train might be described as 30 meters per second, but its velocity is 30 meters per second North.
  • 9. Questions to Discuss
    • What are five types of motion? Give an example for each one.
    • What do you need to know to find an objects velocity?
    • What is a point of reference?
    • If you were riding a bicycle, is your motion constant, variable, or periodic? Explain.
  • 10. Lesson 2 - What are forces?
    • Pushes and Pulls
    • A Force is a push or pull that acts on an object.
      • When one object pushes or pulls another object, the first object is exerting a force on the second one.
    • Forces can make a moving object speed up, slow down, or change direction.
    • Forces have both magnitude and direction.
      • Magnitude is measured in newtons (N).
      • The direction of a force can be described by telling which way the force is acting.
  • 11. Gravity
    • Every object in the universe exerts a gravitational pull on every other object.
    • An object’s weight is the amount of gravitational force between it and Earth.
    • -This depends on the object’s mass and Earth’s mass.
  • 12. Magnetism
    • Magnetism is a force that pushes or pulls on other objects .
    • Magnets will strongly pull on objects made of iron, cobalt, nickel, and gadolinium.
    • The north and south poles of
    • two magnets will push away
    • from each other.
  • 13. Electricity
    • Electric forces act between objects that are electrically charged.
        • Objects get electrically charged when they gain or lose electrons.
    • All atoms have negative electrons and positive protons.
        • If an object gains electrons , the object will be negatively charged.
        • If an object loses electrons, it will be positively charged.
  • 14. Electricity
    • Electrons move from one object to another when:
        • The objects are rubbed together.
    • Objects that are electrically charged will exert forces on each other.
    • Oppositely charged objects are attracted to each other.
    • Objects with the same charge are repelled from each other.
  • 15. Friction
    • Friction is the force that results when two materials rub against each other.
    • Friction acts to slow down the motion of an object or keep it from starting to move.
    • Friction depends on the qualities of the object involved.
        • The shape, speed, or texture of one object can affect the amount of friction.
  • 16. Work
    • Work is done when a force moves an object.
    • To calculate work:
    • Force x Distance = Work
    • Work is measured in joules.
    20 N x 2 m = 40 J 2 m 20 N 10 N x 2 m = 20 J 2 m 10 N 10 N x 1 m = 10 J 1 m 10 N Work Distance Force
  • 17. Work
    • If the force applied to an object, does not make the object move, then no work has been done.
    • Work is only done when the object moves.
    • Holding an object in place can require a force, but since the object doesn’t move no work is done.
  • 18. Power
    • Power is the rate at which work is done .
    • The faster work is done, the power is increased.
    • To calculate the amount of power:
    • Work = Power
    • Time
  • 19. Questions to Discuss
    • What are the causes of electrical and magnetic forces?
    • How does friction affect movement?
    • What are two examples of forces?
    • What kind of force can make a paper clip cling to a comb?
    • In what unit is work measured? In what unit is power measured?
  • 20. Lesson 3 - What are Newton’s laws of motion?
    • NET FORCES
    • Different forces can act on an object at the same time.
    • They may act in the same direction, different directions, and some may be stronger than others.
    • The combination of all these forces is the NET FORCE!
    • The net force determines whether the object start or stop moving or change direction.
  • 21. Net Forces
    • Equal forces working in opposite directions, balance those forces. The net force is zero .
    • This is called equilibrium.
        • A stationary object will remain motionless.
        • A moving object in will continue to move at a constant speed in a straight line.
    • Unbalanced forces acting on an object causes it to change motion.
  • 22. Newton’s First Law
    • Unless a net force acts on an object , the object will remain in constant motion.
    • An object at rest stays at rest until a net force acts upon it.
    • An object moving at a constant speed will continue to move in a straight line and at a constant speed.
  • 23. Newton’s Second Law
    • Acceleration is the rate at which the velocity of an object changes over time.
    • The net forces acting on an object can change an object’s velocity by causing it to speed up, slow down, or change directions.
    • The formula that describes the relationship between force, mass, and acceleration is:
    • Force = Mass x Acceleration
    • The stronger the force the more that object will accelerate.
  • 24. Newton’s Third Law
    • When one object exerts a force on a second object, the second object exerts a force on the first object.
    • This is sometimes called the action-reaction law of motion.
    • Action-reaction forces are always equal and opposite , and they occur in pairs .
  • 25. Questions to Discuss
    • What is the net force on an object?
    • What does an object look like that is in equilibrium?
    • What does Newton’s first law of motion state? The second law? The third law?
    • How does force affect acceleration?
    • Why do action-reaction forces always occur in pairs?
  • 26. Lesson 4 - What are simple machines?
    • Machines and Work:
        • Work is done when a force causes an object to move.
        • A machine is a device that changes the direction or the amount of force needed to do work .
        • Machines do not reduce the amount of work that needs to be done , it just makes it easier .
        • There are four types of simple machines: pulley, wheel and axle, lever, inclined plane
  • 27. Pulley
    • A pulley consists of a rope or cable that runs through a grooved wheel.
    • *Examples:
    • flag pole
    • drapery rods
  • 28. Wheel and Axle
    • A wheel and axle is made up of a circular object and a shaft.
    • *Examples:
    • steering wheel
    • door knob
  • 29. Lever
    • A lever is made up of a stiff bar that rotates around a fixed point called a fulcrum .
    • *Examples:
    • tongs
    • clothes pins
    • pliers
  • 30. Inclined Planes
    • An inclined plane consists of a flat surface with one end higher than the other.
    • *Examples:
    • screws, wedge, doorstop
    • ramps,
  • 31. Complex Machines
    • A complex machine uses two or more simple machines put together .
    • Many complex machines use electricity, gravity, burning fuel, human force, or magnetism to operate
        • Examples:
        • washing machine
        • go cart
        • car
        • s ailboat
  • 32. Questions to Discuss
    • Why is a screw considered a simple machine?
    • What is a complex machine?
    • How is the movement of rolling a weight up an inclined plane different from climbing stairs?
    • What is a machine?
    • List the four simple machines. What is one example of each simple machine?