Lesson 20

• Any change that occurs requires energy• Energy is the ability to do work or cause change

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Work

• Work is the application of a force to an object to move it a certain distance in the direction of the force* Work = force x distance or w= f x d

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Work

• Work is not always done when a force is applied to an object• Work is done only when an object moves in the same direction of the force that is being applied

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Work

• For example, you may get tired after carrying your backpack all day at school

• However, you did not do any work to carry your backpack• The force you applied was in an upward direction to keep the backpack from falling to the ground

4

Work

• The backpack moved in a forward, not upward direction as you walked through school

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Work

• Now picture a person wearing a backpack and climbing up the side of a mountain• The person is doing work because the direction of motion and the force being applied are both upward.

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Simple Machines

• A machine is a device that makes work easier by changing the size or direction of a force

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Simple Machines

• There are six types of simple machines:1.Lever2.Inclined plane3.Wheel and axle4.Wedge5.Pulley6.screw

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Simple Machines

• Complex machines are made from a combination of these six simple machines

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Inclined Plane

• An inclined plane is a straight, slanted surface• A ramp is an example of a stationary inclined plane• An inclined plane makes work easier because it is easier to push an

object up a ramp than it is to lift the same object straight up to the same height

10

Wedges and Screws

• Wedges and screws are examples of inclined planes that move• A wedge is an inclined plane that is wider or thicker at one end than at the other

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Wedges and Screws

• A wedge makes work easier because, when moved, a wedge is used to cut, split, or pry apart objects

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Wedges and Screws

• A screw is an inclined plane that is wrapped around a cylinder• When a screw is turned, a small force is applied over the long distance of the screw’s threads

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Wedges and Screws

• A screw makes work easier depending on the number of threads, which in turn depends on the length of the inclined plane wrapped around the center

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Levers

• A lever is a simple machine made up of a bar that pivots at a fixed point called a fulcrum• The force applied to a lever is called the effort• The object moved is the load

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Levers

• Levers make work easier in three different ways, and levers are therefore classified into three groups

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Levers

• These three groups are based upon the locations of the fulcrum, effort, and load• In a first class lever, the fulcrum is located between the effort and the load

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Levers

• In a second class lever, the load is located between the fulcrum and the effort• In a third class lever, the effort is applied between the fulcrum and the load

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Pulleys

• A pulley is a rope or chain wrapped around a wheel• A load is attached to one end of the rope• A force is applied to the other end of the rope

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Pulleys

• Pulley systems can consist of one or more fixed pulleys, one or more moveable pulleys, or both fixed and moveable pulleys making a combined pulley system

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Wheel and Axles

• A wheel and axle is a simple machine that consists of two circular objects of different sizes• The wheel is always larger than the axle

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Wheel and Axles

• A wheel and axle makes work easier by getting more force from the effort put in when compared to the amount of distance

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Wheel and Axles

• When effort is applied to move the wheel, the axle turns a shorter distance, but it moves with a more powerful force

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