# Lesson 20 Any change that occurs requires energy

## Presentation on theme: "Lesson 20 Any change that occurs requires energy"— Presentation transcript:

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

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

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

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

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

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.

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

Simple Machines There are six types of simple machines: Lever
Inclined plane Wheel and axle Wedge Pulley screw

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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