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Lesson 20 Any change that occurs requires energy Energy is the ability to do work or cause change 1.

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Presentation on theme: "Lesson 20 Any change that occurs requires energy Energy is the ability to do work or cause change 1."— Presentation transcript:

1 Lesson 20 Any change that occurs requires energy Energy is the ability to do work or cause change 1

2 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 2

3 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 3

4 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

5 Work The backpack moved in a forward, not upward direction as you walked through school 5

6 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. 6

7 Simple Machines A machine is a device that makes work easier by changing the size or direction of a force 7

8 Simple Machines There are six types of simple machines: 1.Lever 2.Inclined plane 3.Wheel and axle 4.Wedge 5.Pulley 6.screw 8

9 Simple Machines Complex machines are made from a combination of these six simple machines 9

10 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

11 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 11

12 Wedges and Screws A wedge makes work easier because, when moved, a wedge is used to cut, split, or pry apart objects 12

13 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 13

14 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 14

15 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 15

16 Levers Levers make work easier in three different ways, and levers are therefore classified into three groups 16

17 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 17

18 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 18

19 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 19

20 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 20

21 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 21

22 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 22

23 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 23


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