Chapter Introduction Lesson 1Lesson 1Work and Power Lesson 2Lesson 2Using Simple Machines Chapter Wrap-Up

How do machines make doing work easier?

Essential Questions What is the relationship between work, power and efficiency? Work and Power

Work Power Efficiency Work and Power

In science, work is what is necessary for a force to move an object through a distance. What is work? Work is calculated by multiplying the force applied to an object by the distance the object moves.

In order for you to do work, two things must occur: –You must apply a force to an object. –The object must move in the same direction as your applied force. What is work? (cont.)

Is work being done? –Pushing a grocery cart in a store? Yes, because the cart is moving in the same direction as the force (push). –Standing and holding a bag of groceries? No, Although you are applying a force to the grocery bag by holding it, the grocery bag is not moving so no work is done. What is work? (cont.)

Work is important in science because it is related to energy. Work done when you lift an object which also increases the object’s energy. –Moving objects have kinetic energy –Gravitational Potential Energy (GPE) of an object increases as its height above the ground increases. What is work? (cont.)

Doing work on a tray transfers energy to the tray. The added energy can be either kinetic energy or potential energy. What is work? (cont.)

How is work measured? (cont.) Work is equal to the force of a push or a pull multiplied by the distance the object is moved. The product of force and distance has the unit newton·meter. The newton· meter is also known as the joule (J).

How is work measured? (cont.)

The work done on an object depends on the direction of the force applied and the direction of the motion. How is work measured? (cont.) Applied Force Motion of bed

Now think of a box being pulled by a rope. –In this scenario, the applied force is at an angle (from your arm to the rope). The applied force has a horizontal part and a vertical part. How is work measured? (cont.) Applied force Horizontal force Vertical force Motion of the box

When the applied force and the motion of the object are NOT in the same direction, only the part of the force that is in the same direction as the motion of the object is used in the work equation. The vertical part of the applied force does no work on the box because it is not in the same direction as the motion of the box. Motion of the box Horizontal force Vertical force How is work measured? (cont.)

The work done to lift an object equals the weight of the object multiplied by the distance it is lifted. –Work = weight x distance How is work measured? (cont.)

Power is the amount of work done per unit of time. You can also think of power as how fast energy is transferred to an object. What is power?

You can calculate power by dividing the work done by the time needed to do the work. Power is expressed in joules per second(J/s). One Joule per second is also know as a watt (W). What is power? (cont.)

A machine is any device that makes doing something easier. Some machines are simple and other machines are more complex. What is efficiency?

The force you apply to a machine is the input force. The machine changes the input force to an output force. What is efficiency? (cont.) Input force Output force

The amount of input force multiplied by the distance over which the input force is applied is the input work. W input = F input x d input What is efficiency? (cont.) Input force Distance applied

Machines convert input work to output work by applying an output force on something and making it move. –W output = F output x distance output What is efficiency? (cont.) Output force Output distance

The output work done by a machine never exceeds the input work because of friction. –Friction converts some of the input work to thermal energy. What is efficiency? (cont.)

Efficiency is the ratio between the work done by a machine and the work put into it. Because output work is always less than input work, a machine’s efficiency is always less than 100 percent. –Ex. Elevators are 85% efficient, car motors are 17% efficient What is efficiency? (cont.)

When you lift an object, what else are you doing? A.decreasing the object’s energy B.increasing the object’s energy C.making the object do work D.receiving the object’s energy

A.energy B.force C.power D.work Which is the rate at which work is done?

A.distance the object is lifted B.energy used to lift the object C.force applied to the object D.power needed to lift the object To calculate the work done lifting an object, which is multiplied by the weight of the object?

Essential Question What is the relationship between work input and work output in a simple machine? Using Simple Machines

Simple machine Mechanical advantage Lever Fulcrum Using Simple Machines Wheel and axle Pulley Inclined plane Screw Wedge

Simple machine is a device with few, if any, moving parts that makes it easier to do work. –Ex. screwdriver A machine makes work easier by changing the size of the force, the distance the force acts, or the direction of a force. What is a simple machine?

The two main classes of simple machines are the lever and the inclined plane. Lever class includes: –Wheel and axle and the pulley What is a simple machine? (cont.)

Inclined plane includes: –Wedge and screw What is a simple machine? (cont.)

Mechanical advantage is the number of times a simple machine multiplies an effort force. What is a simple machine? (cont.)

Mechanical advantage can be less than 1, equal to 1, or greater than 1. A mechanical advantage greater than 1 means the output force is greater than the input force. What is a simple machine? (cont.)

Lever is a simple machine consisting of a bar and a pivot point. –Fulcrum is the pivot point in a lever. The part of the bar on which a person applies an effort force is called the effort arm. What are the three kinds of levers?

The part of the bar on which the lever produces an output force is called the resistance arm. The position of the fulcrum, the effort arm and the resistance arm vary among levers. What are the three kinds of levers? (cont.)

In a first-class lever, the fulcrum is between the input force and the output force. The direction of the input force is opposite the direction of the output force. When the effort arm is longer than the resistance arm, the output force is greater than the effort force What are the three kinds of levers? (cont.)

Your neck is an example of a first-class lever. What are the three kinds of levers? (cont.)

A second-class lever has the output force between the input force and the fulcrum. The output force and the input force act in the same direction. A second-class lever makes the output force greater than the input force. What are the three kinds of levers? (cont.)

A wheel barrow is an example of a second-class lever. What are the three kinds of levers? (cont.)

A third-class lever has the input between the output force and the fulcrum. The output force is less than the input force. Both the input force and the output force act in the same direction. What are the three kinds of levers? (cont.)

A fishing rod is an example of a third- class lever. What are the three kinds of levers? (cont.)

The ideal mechanical advantage of a lever equals the length of the input arm divided by the length of the output arm. What are the three kinds of levers? (cont.)

Wheel and axle is a simple machine that consists of a wheel that applies an effort force and a smaller axle that produces an output force. Mechanical advantage of a wheel and axle is calculated by dividing the length of the effort arm by the length of the resistance arm. What other machines are like levers?

For a wheel and axle, the length of the input arm is the radius of the wheel and the length of the output arm is the radius of the axle. A screwdriver is a wheel and axle. The handle is the wheel and the shaft is the axle. What other machines are like levers? (cont.)

A wheel and axle can also make work easier in another way. –If the radius of the wheel is smaller than the radius of the axle, the output distance is increased and the output force is decreased. –Ex. Helicopters and ceiling fans. What other machines are like levers? (cont.)

Pulley is a grooved wheel that turns by the action of a rope in the groove. What other machines are like levers? (cont.) In a pulley, the rope forms the arms and the wheel serves as the fulcrum.

A pulley can be fixed or movable. What other machines are like levers? (cont.) A fixed pulley makes work easier by changing the direction of the effort force.

Movable pulleys are attached to the object being lifted and decrease the force needed to lift the object. A single movable pulley multiplies the effort force by 2, so it has a mechanical advantage of 2. A single movable pulley does not change the direction of the effort. What other machines are like levers? (cont.)

The ideal mechanical advantage of a pulley or a pulley system is equal to the number of sections of rope supporting the object. What other machines are like levers? (cont.)

Inclined plane is a straight, slanted surface that can multiply an effort force. It takes less force to move an object upward along an inclined plane than it does to lift the object straight up. What are inclined planes?

The mechanical advantage of a ramp is equal to the output force divided by the effort force. What are inclined planes? (cont.)

The ratio of output force to effort force is the same as that of effort distance to output distance. For this reason, a ramp’s mechanical advantage can also be found by dividing the length of the incline by its height. What are inclined planes? (cont.)

Calculate the mechanical advantage of each inclined plane. What are inclined planes? (cont.) Length = 2.0m, height = 1.0m IMA = 2 ÷ 1 = 2 Length = 5.0m, height = 3.0m IMA = 5.0 ÷ 3.0 = 1.7 The longer and shallower the ramp, the greater the mechanical advantage.

Screw is a simple machine made of an inclined plane wrapped around a central bar that can multiply an effort force. What are inclined planes? (cont.) Spiral ridges called threads move into an object as the head of the screw turns. The space between the threads is called the pitch.

The mechanical advantage of a screw and ramp are calculated in a similar way. What are inclined planes? (cont.) IMA = effort distance output distance The effort distance is the distance around the head and the output distance is the pitch of the screw.

Wedge is an inclined plane that changes the direction of an applied force. A wedge can be a single inclined plane or two inclined planes joined back to back. The thinner the wedge, the greater the mechanical advantage. What are inclined planes? (cont.)

When two or more simple machines are combined, they form a compound machine. What are compound machines? Levers, screws, wheels and axles and gears combine to make a bicycle, a compound machine.

The efficiency of a compound machine is calculated by multiplying the efficiencies of each simple machine together. Each simple machine decreases the overall efficiency of the compound machine. Lubricants, such as oil, reduce the amount of energy that is wasted as heat. What are compound machines? (cont.)

What are levers, wheels and axles, inclined planes, wedges, screws, and pulleys examples of? A.complex machines B.compound machines C.idea machines D.simple machines

A.fulcrum B.inclined plane C.screw D.wheel Which uses less force to raise an object compared to lifting the object straight up?

A.gear B.pulley C.screw D.wedge Which is a simple machine consisting of a grooved wheel with a rope or cable wrapped around it?

Visual Summary Chapter Review Standardized Test Practice

A machine makes work easier by changing the force that is needed or the direction or the distance through which a force is applied.

For work to be done on an object, an applied force must move the object. When work is done on an object, the energy of the object increases. Power is the rate at which work is done. Because of friction, the output work done by a machine is always less than the input work to the machine. Friction between moving parts converts some of the input work into thermal energy and decreases the efficiency of the machine. Lesson 1: Work and Power

Lesson 2: Using Simple Machines Simple machines make it easier for people to do work. They have few, if any, moving parts. Machines make work easier by changing the size of the force required, the distance over which the object moves or the direction of the required force. The mechanical advantage of a machine is the ratio of the output force to the input force. A compound machine is made of two or more simple machines that operate together.

A.distance and length B.force and distance C.force and power D.height and weight What two things must you know to calculate work?

A.distance B.force C.time D.weight What do you divide work by to calculate power?

A.energy B.input force C.output force D.power Which refers to the force you apply to a machine to make it work?

A.output power B.output force C.mechanical advantage D.input force What does a machine apply to an object?

A.axle B.fulcrum C.screw D.wedge What does a lever rotate around?

A.distance B.energy C.force D.power What is transferred when work is done?

A.power B.force of the motion C.distance of the motion D.direction of the motion The work done on an object depends on the direction of the force applied and which of these?

A.efficiency B.equal output C.mechanical advantage D.output work What is the ratio of a machine’s output force to its input force?

A.fulcrum B.lever C.wedge D.wheel and axle What is a simple machine made of a bar that rotates about a fixed point?

A.wedge B.screw C.fulcrum D.axle What term describes an inclined plane wrapped around a cylinder?