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Force, motion, and machines

Force, motion, and machines. Force of gravity. Gravity is a force that pulls objects toward each other. All matter has gravity. Force of gravity. 2 main things affect how gravity pulls on an object: The objects mass (more mass = more pull from gravity)

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Force, motion, and machines

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  1. Force, motion, and machines

  2. Force of gravity • Gravity is a force that pulls objects toward each other. • All matter has gravity

  3. Force of gravity • 2 main things affect how gravity pulls on an object: • The objects mass (more mass = more pull from gravity) • Example: Why do the planets orbit the sun. • The distance between the two objects (The further the distance = less pull from gravity.) • Example: Why does the moon orbit the earth?

  4. Weight and mass • Mass is a measurement of how much matter is in something. • Weight is a measurement of how gravity is pulling down on something. • Weight is affected by gravity, mass is not!

  5. Laws of motion • Isaac Newton came up with 3 laws of motion in the late 1600s.

  6. Laws of motion • The first law of motion says that an object at rest will stay at rest, and an object in motion will stay in motion unless it is acted upon by a force. • Inertia is when an object resists change in motion. • The more mass something has, the more inertia it has.

  7. Friction • Friction is the force created when two surfaces rub against each other.

  8. Friction • There are 4 main types of friction • Static friction • Sliding friction • Rolling friction • Fluid friction

  9. Friction • Some devices use friction to control the motion of an object.

  10. Simple Machines • A machine makes work easier by changing one of 3 things: • The amount of force you have to put out. • The distance you use the force over. • The direction of the force.

  11. Simple Machines • A machine’s mechanical advantage is the number of times that a machine increases a force. • (Example: if it makes your job 3 times easier, it would have a mechanical advantage of 3)

  12. Simple Machines • There are 6 types of simple machines: • Inclined plane • Wedge • Screw • Lever • Wheel and axel • Pulley

  13. Simple Machines – inclined plane • An inclined plane is a flat sloped surface. (Like a ramp). • An inclined plane lets you exert your force over a longer distance. • Where in the school would you find inclined planes?

  14. Simple Machines – inclined plane • You can find the mechanical advantage of an inclined plane by using the formula: • Length of incline/height of incline.

  15. Simple Machines – wedge and screw • A wedge and a screw are other simple machines that are made from an inclined plane. • Where are some places in the school that you might find wedges and screws?

  16. Simple machines - Levers • A lever is a rigid bar that is free to rotate or pivot on a fixed point. • The point that the lever rotates on or around is called the fulcrum. • Levers change the amount of force you have to put out, and they can change the direction of the force.

  17. Simple machines - Levers • First class lever: • A first class lever has the fulcrum in the middle. • Examples of first class levers include: • Prying open a paint can • Scissors • Rowing a boat • Pliers

  18. Simple machines - Levers • A second class lever has the resistance (load) in the middle. • Examples of second class levers include: • Wheelbarrows • Nutcrackers

  19. Simple machines - Levers • A third class lever has the effort in the middle • Examples of third class levers include: • Brooms • Tweezers • Tongs • Fishing poles • Hockey sticks

  20. What type of lever is this?

  21. Simple machines - Levers • You can find the mechanical advantage of a lever using the formula: • Distance from the fulcrum to the input force / Distance from the fulcrum to the output force. • Input force is sometimes called “Effort” • Output force is sometimes called “load” or “resistance”

  22. ? Calculate the mechanical advantage for the levers

  23. Simple machines – Wheel and axle • A wheel and axle is made of 2 cylinders of different sizes that rotate together. • A wheel and axle changes the distance over which a force is exerted. • Examples include: • Screwdriver • Doorknob • A faucet

  24. Simple machines – pulleys • A pulley is made of a grooved wheel with a rope wrapped around it. • Pulleys change the amount of force needed and the direction of the force. • Where might you find pulleys at the school?

  25. Simple machines – pulleys • The mechanical advantage for a pulley is found by counting the number of rope segments (not counting the one that is attached to the effort.)

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