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Work & Power
Work is defined as the transfer of energy when a force causes an object to move. Power is the rate at which work is done and is calculated by dividing the work by the time taken. Machines make work easier by changing the direction or magnitude of the applied force, allowing tasks to be completed with less exertion. They do not reduce the total amount of work done.
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Work & Power
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- 2. Work Work :the transfer of energy that occurs when a force moves an object. an object must move a force must act on the object in the direction the object moves If a force is applied without movement occurring, NO WORK IS DONE!
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- 4. If 10 Nof force is applied to this cart, moving it 20 m, how much work is done? W = F x d W = 10 N 20 m W = 200 N m Joule = 1 N force that moves an object 1 m W = 200 J
- 5. Energy Mechanical energyis related to work: The ability to do work or The amount of work done Has same units as work (Joules)
- 6. Power Power : the rate at which work is done. Power = work/time Power = Force distance time Joules/second = Watts
- 7. Calculating Power Todunk a ball, the player must place 25 N of force on a ball to lift it to the net. The distance from ground to rim is 10 feet. What is the work done per dunk? Work = 25 N x ? meters Work = 75 Joules What is the power of a player who can dunk in 3 seconds? Power = 75J ÷ 3s Power = 25 Watts
- 8. Work & MachinesA machine makes work easier by changing the direction or size of the force needed to move an object. (They cannot save or reduce work) W = Force x distance
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- 10. Intro to MachinesA machine is a device that makes work easier.
- 11. Simple Machines Allmachines are made up of one or more of these 6 basic tools Each one reduces the amount of force needed to accomplish work.
- 12. Compound Machines Sometools have two or more simple machines working together. scissors 2 levers joined at fulcrum blades are wedges bicycle two wheel and axel machines screws (hold frame together) levers (pedals and hand brakes) wheel barrow : two levers wheel & axle
- 13. Review What ispressure? Amount of force applied to a unit of area. What formula do we use to calculate pressure? P = F/A What units are used to measure pressure? pascals (Pa) N/m 2 What is Pascal’s Principle? A force applied to a fluid in a closed container will cause an increase in pressure, equally transmitted to all parts of the fluid. How does depth affect pressure? Pressure also increases with depth.
- 14. Review Newton’s LawsExplanation Summary First Second Third
Editor's Notes
- #8 10 ft = 3 meters
- #11 Discuss with children how they use machines to make work easier. You may want to identify machines children use often such as a bus, a stapler, or a bike. While machines can have many moving parts, a simple machine has none or very few moving parts. Explain to children that a force is a push or pull that can change the way something moves. For example, when you throw a ball you use a force to make it move. When you catch a ball, you use a force to stop its motion. Any push or pull is a force. Review with children that heavier objects require more force to move. For example, a bowling ball is harder to throw than a table tennis ball. Some objects are so heavy that people need machines to use them. A simple machine can change the direction or significance of a force in different ways to make work easier. It can change the way a force is used to make it more effective. A ramp, or inclined plane, is a simple machine with a slanted surface. It helps people and things move between higher and lower places. Discuss different ramps children have seen or used, such as moving ramps, disabled accessibility ramps, or slides on the playground. Explain that it takes a lot of force to lift and move something heavy, but it’s much easier to push it up a ramp. It is much harder to move things up steeper ramps, or ramps that go up higher, just as it is harder for people to walk up a bigger or steeper hill. A lever is a simple machine that consists of a bar that rests on a fulcrum, or a point that does not move. A lever can also help lift up heavy loads. A seesaw is the classic example of a lever. When force is applied to one side and is pushed down, the other side lifts up. Any tool that pries something loose is a lever, like the claw side of a hammer or a bottle opener. Scissors and staplers are common items that use levers. A wheel and axle work together to make a simple machine. Explain that a wheel turns around a rod, called an axle. A wheel and axle can help move things faster or more easily, and also help things turn. Carts, skateboards, roller skates, bikes, and cars all use wheels and axles. Explain that heavy things can be difficult to push across a surface and can require a lot of force. But, if you add wheels to the bottom, it becomes much easier. Wheels and axles can act as fulcrums, as well. A wheelbarrow can lift and carry very heavy items using wheels as rotating fulcrum points. Have children give examples of how wheels and axles make work easier. A pulley is a simple machine that has a rope or cable that goes over a wheel. A pulley helps people lift things up and change the direction of their force. You pull on a rope to make the load go up. You can also connect pulleys together, creating a combined pulley that requires less than half the force otherwise needed to lift up a load. Clotheslines, flagpoles, and blinds use pulleys. Help children understand that combining simple machines can also make work easier. Any two or more simple machines put together are known as compound machines. Many machines are compound machines. For example, a crane uses levers, wheels and axles, and many pulleys to lift up heavy objects. Learning about simple machines and forces is a great way to teach the fundamentals of physics and help children understand the world around them.