How do machines make doing work easier What

How do machines make doing work easier?

What do you think? Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements.

Do you agree or disagree? 1. Work is done when you push a book across a table. 2. Doing work faster requires more power. 3. Machines always decrease the force needed to do a job.

Work and Power • What must happen for work to be done? • How does doing work on an object change its energy? • How are work and power related?

What is work? 1. In science, work is the transfer of energy that occurs when a force makes an object move. 2. A force that does not make an object move does no work.

What is work? (cont. ) 1. Stand up and push down on your table with all the force you can. 2. Lift your chair slowly up from the ground to above your head. 3. Hold your chair above your head. When were you doing work?

Calculating Work • To calculate work, multiply the force applied to the object by the distance the object is moved by that force. • The product of force and distance has the unit newton·meter. The newton· meter is also known as the joule (J).

Calculating Work (cont. ) How is work done?

The work done on an object depends on the direction of the force applied and the direction of the motion. Hutchings Photography/Digital Light Source

When the force and the motion are in the same direction, calculate work by multiplying the force and the distance. Hutchings Photography/Digital Light Source

When the applied force and the motion of the object are NOT in the same direction, the applied force can be thought of as being two forces acting on the object at the same time. Hutchings Photography/Digital Light Source

• When the applied force and the motion of the object are NOT in the same direction, only the horizontal part of the applied force is used in the work equation. • The vertical part of the applied force does no work on the suitcase. Hutchings Photography/Digital Light Source

The work done to lift an object equals the weight of the object multiplied by the distance it is lifted. Hutchings Photography/Digital Light Source

Work and Energy • Doing work on an object transfers energy to the object. • This helps scientists predict how an object will act when forces are applied to it. • Work done when you lift an object also increases the object’s energy.

Doing work on a tray transfers energy to the tray. The added energy can be either kinetic energy or potential energy.

Work and Energy (cont. ) How does doing work on an object change its energy?

What is power? • Power is the rate at which work is done. • You can also think of power as how fast energy is transferred to an object.

What is power? (cont. ) power Science Use the rate at which work is done Common Use the ability to accomplish something or to command or control other people

What is power? (cont. ) You can calculate power by dividing the work done by the time needed to do the work.

What is power? (cont. ) How are work and power related?

• Work is done on an object when the object moves in the direction of the applied force. • When work is done on an object, energy is transferred to the object. Hutchings Photography/Digital Light Source

• To increase power, work must be done in less time. Hutchings Photography/Digital Light Source

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

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

To calculate the work done lifting an object, which is multiplied by the weight of the object? 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

Do you agree or disagree? 1. Work is done when you push a book across a table. 2. Doing work faster requires more power.

Using Machines • What are three ways a machine can make doing work easier? • What is mechanical advantage? • Why can’t the work done by a machine be greater than the work done on the machine?

Using Machines • mechanical advantage • efficiency

What is a machine? • A machine is any device that makes doing something easier. • Some machines are simple and other machines are more complex. Gabe Palmer/Alamy

What is a machine? (cont. ) • Machines make tasks easier, but do not decrease the amount of work required. • A machine changes the way in which the work is done. Royalty-Free/CORBIS S. Alden/Photo. Link/Getty Images

What is a machine? (cont. ) • The force you apply to a machine is the input force. • The machine changes the input force to an output force. The Mc. Graw-Hill Companies

What is a machine? (cont. ) The amount of input force multiplied by the distance over which the input force is applied is the input work. The Mc. Graw-Hill Companies

What is a machine? (cont. ) Machines convert input work to output work by applying an output force on something and making it move. The Mc. Graw-Hill Companies

How do machines make work easier to do? A machine makes work easier by changing the size of the force, the distance the force acts, or the direction of a force. The Mc. Graw-Hill Companies

How do machines make work easier to do? (cont. ) When the output force is greater than the input force, the output force acts over a shorter distance. Steve Gorton/Dorling Kindersley/Getty Images

Machines make work easier in three ways:

When the output force acts over a longer distance than the input force, the output force is less than the input force. Sean Justice/Getty Images

Machines make work easier in three ways:

Equal output and input forces act over equal distances.

Machines make work easier in three ways:

How do machines make work easier to do? (cont. ) In what three ways do machines make doing work easier?

What is mechanical advantage? A machine’s mechanical advantage is the ratio of a machine’s output force to the applied input force.

What is mechanical advantage? (cont. ) The mechanical advantage tells you how many times larger or smaller the output force is than the input force. mechanical from Greek mechanikos, means “machine”

What is mechanical advantage? (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. • The ideal mechanical advantage is the mechanical advantage if no friction existed.

What is mechanical advantage? (cont. ) What is mechanical advantage?

What is efficiency? • The output work done by a machine never exceeds the input work of the machine. • Friction converts some of the input work to thermal energy and this converted energy cannot be used to do work.

What is efficiency? (cont. ) • The efficiency of a machine is the ratio of the output work to the input work. • Because output work is always less than input work, a machine’s efficiency is always less than 100 percent.

What is efficiency? (cont. ) Why can’t the work done by a machine be greater than the work done on the machine?

• A machine makes a task easier and it can be simple or complex. • The mechanical advantage of a machine indicates how it changes an input force. The Mc. Graw-Hill Companies

• The efficiency of a machine is increased when a lubricant coats moving parts.

Which is the product of the output force and the distance over which the output force is applied? A. machine B. input work C. output work D. mechanical advantage

How can a machine NOT make work easier? A. change the direction of the input force B. decrease the input force C. increase the amount of work done D. increase the input force

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

Do you agree or disagree? 3. Machines always decrease the force needed to do a job. 4. A well-oiled, low-friction machine can be 100 percent efficient.

Simple Machines • What is a simple machine? • How is the ideal mechanical advantage of simple machines calculated? • How are simple machines and compound machines different?

Simple Machines • simple machine • inclined plane • lever • wedge • fulcrum • screw • wheel and axle • pulley

What is a simple machine? • Six types of simple machines do work using only one movement. • lever • wheel and axle • inclined plane • wedge • screw • pulley

What is a simple machine? (cont. ) Describe a simple machine.

Levers • A lever is a simple machine made up of a bar that pivots, or rotates, about a fixed point. • The point about which a lever pivots is called a fulcrum. Steve Gorton/Dorling Kindersley/Getty Images

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.

Levers (cont. ) A finger tab on a beverage can is a firstclass lever. Jupiterimages

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.

Levers (cont. ) A wheel barrow is an example of a secondclass lever. Digital Vision / Alamy

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.

Levers (cont. ) A rake is an example of a third-class lever. Doug Menuez/Getty Images

Levers (cont. ) The ideal mechanical advantage of a lever equals the length of the input arm divided by the length of the output arm.

Mechanical Advantage of Levers

Mechanical Advantage of Levers

Mechanical Advantage of Levers

Levers (cont. ) How is the ideal mechanical advantage of a lever calculated?

Levers (cont. ) The neck, foot, and arm are examples of first-, second-, and third-class levers in the human body.

Wheel and Axle • A wheel and axle is an axle attached to the center of a wheel and both rotate together. • 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. Don Tremain/Getty Images

Wheel and Axle (cont. ) A screwdriver is a wheel and axle. The handle is the wheel and the shaft is the axle.

Wheel and Axle (cont. ) Even though no machine is 100% efficient, you can calculate the ideal mechanical advantage of a wheel and axle.

Inclined Planes • A ramp, or inclined plane, is a flat, sloped surface. • It takes less force to move an object upward along an inclined plane than it does to lift the object straight up.

Moving a sofa is easier using a ramp. Using a ramp only requires a 100 -N force to move the 500 -N sofa. Because of friction, no ramp operates at its ideal mechanical advantage.

Inclined Planes (cont. ) The ideal mechanical advantage of an inclined plane equals its length divided by its height.

Inclined Planes (cont. ) • The longer or less-sloped an inclined plane is, the less force is needed to move an object along its surface. • A sloped surface that moves is called a wedge. • A wedge is really a type of inclined plane with one or two sloping sides.

Inclined Planes (cont. ) • A screw is an inclined plane wrapped around a cylinder. • When you turn a screw, the screw threads change the input force to an output force and the output force pulls the screw into the material.

Pulleys A pulley is a simple machine that is a grooved wheel with a rope or a cable wrapped around it.

Pulleys (cont. ) A fixed pulley only changes the direction of the force.

Pulleys (cont. ) Movable pulleys are attached to the object being lifted and decrease the force needed to lift the object.

Pulleys (cont. ) A pulley system is a combination of fixed and movable pulleys that work together.

Pulleys (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 is a compound machine? Two or more simple machines that operate together form a compound machine. How are simple machines and compound machines different?

What is a compound machine? (cont. ) • A gear is a wheel and axle with teeth around the wheel. • Two or more gears working together form a compound machine. Brand X Pictures

What is a compound machine? (cont. ) • When the teeth of two gears interlock, turning one gear causes the other to turn. • Gears of different sizes turn at different speeds. CORBIS

What is a compound machine? (cont. ) • 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.

• Six simple machines are the lever, wheel and axle, inclined plane, wedge, screw, and pulley. • All levers rotate, or pivot, about the fulcrum. • The kind of wedge used to split logs is a simple machine.

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

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

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

Do you agree or disagree? 5. A doorknob is a simple machine. 6. A loading ramp makes it easier to lift a load.

Key Concept Summary Interactive Concept Map Chapter Review Standardized Test Practice

A machine makes work easier by changing the size of the applied force, changing the distance over which the applied force acts, or changing the direction of the applied force.

Lesson 1: Work and Power • For work to be done on an object, an applied force must move the object in the direction of the force. • When work is done on an object, the energy of the object increases. • Power is the rate at which work is done. Hutchings Photography/Digital Light Source

Lesson 2: Using Machines • A machine can make work easier in three ways: changing the size of a force, changing the distance the force acts, or changing the direction of a force. The Mc. Graw-Hill Companies • The mechanical advantage of a machine is the ratio of the output force to the input force. • 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 3: Simple Machines • A simple machine does work using only one movement. • The ideal mechanical advantage of simple machines is calculated using simple formulas. • A compound machine is made up of two or more simple machines that operate together.

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

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

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

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

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

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

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

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

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

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