Work, Power, and Simple Machines

The transfer of energy to an object by the application of a force that causes the object to move in the direction of the force.

work

Work is calculated by multiplying the ________ times the ________ that the object moves.

Force , distance

What is the unit for Force? The Newton

What is the unit for distance? The Meter

What is the unit for Work? Newton meters, (Nm) : Joules (J)

What is the total work done to an object that does not move?

Zero Joules

How much work does a person do if they provide 20 N of force to an object to move it 2 meters?

W = Fd (20)(2) = 40 Joules

How much work is done to an object that you hold above your head for half an hour?

Zero Joules because you are not moving it a distance.

The rate at which work is done. Power

What is the equation for Power? P = W/t

What is the unit for Power? J/s or the Watt (W)

How do machines make work easier? They change the size of the input force, or

the direction of the applied force, or both.

A quantity that represents how much a machine multiplies force or distance.

Mechanical advantage

How is mechanical advantage calculated? It is the ratio of output force to input force. MA = output force/input force

A machine with a mechanical advantage of one or less than one does not multiply the input force. Why then is it still useful?

It may increase the speed or distance.

A short ramp and a long ramp both reach a height of 1 m to load a washing machine. Which ramp has the greater mechanical advantage?

The longer ramp.

How can a ramp make lifting a box easy without changing the amount of work done?

The ramp distributes the force input over a longer distance. The force is less, but the work to reach that same height is still the same. (Neglecting the additional work in the x-direction)

Determine if work is being done in the following situations:

Lifting a spoon of soup. yes Holding a large stack of books over your

head. no Letting a pencil fall to the ground. yes

The most basic types of machines are called _________ _______.

Simple machines

What are the six types of simple machines? Lever, pulley, wheel and axle, inclined

plane, wedge, and screw

Where is the fulcrum located for a first class lever?

In the center

Where is the fulcrum located for a second or third class lever?

On one of the ends

What type of lever has the fulcrum on the end and the output force in the center?

A second class lever

What type of lever has the fulcrum on one end and the output force on the other?

A third class lever

The rigid arm of a lever that turns around on a point.

Fulcrum

Pulleys are modified ________. levers

What is the term for the force that you put in to using a machine?

Effort force

If you were using a machine, what force would you work against?

Resistance force

The distance through which the effort force moves is the _______ ________.

Effort distance

The distance that the resistance force moves through is the _________ __________.

Resistance distance

How would you increase the mechanical advantage of an inclined plane?

Increase the length of the plane.

What determines the class of a lever? The location of the fulcrum and where the

fulcrum Is located to the resistance force.

A push or a pull. Force

A measure of how much work put into a machine is changed to useful work put out by the machine.

efficiency

A type of machine made up of two or more simple machines.

Compound machine.

The distance from the center of a circle to the edge.

radius

A fixed pulley changes the ______ of a force. Direction

A force that opposes motion. Friction

A simple machine made up of two inclined planes.

A wedge

An inclined plane wrapped around a cylindrical post.

a screw

The work done TO a machine is the _______ work.

Input work

A machine in which the input work is equal to the output work is an _______ machine.

Ideal

A device that does work with only one movement is a _______ ________.

Simple machine

The work done BY a machine is the _______ work.

Output

A doorknob is an example of a ___________. Wheel and axle

A grooved wheel with a rope or a chain running along the groove is a __________.

Pulley

A system of pulleys. A block and tackle

Wout / Win * 100 = ___________

Efficiency

The mechanical advantage of a simple fixed pulley is always equal to ______.

one

How do you calculate the ideal mechanical advantage of an inclined plane?

MA = l/h

How do you calculate the ideal mechanical advantage of a wheel and axle?

MA = radius of wheel / radius of axle

What is the conversion factor between horsepower and watts?

1 hp = 746 Watts

How are work and energy related? Work is a form of energy. It takes energy to

perform work. They have the same units. Energy is always transferred from the object doing the work to the object on which the work is being done.

The amount of energy the machine transfers to the object cannot be ________ than the amount of energy transferred to the machine.

Greater

The efficiency of a machine is always ____ than 100%.

less

A modified form of a wheel and axle. A gear

Identify the type of lever.

An Enterprise Bottle Opener First Class

Pliers

First Class

A Broom

Third Class (sometimes first)

A fishing pole

Third Class

A Seesaw

First Class

A wheelbarrow

Second Class

A Baseball Bat

Third class

A hammer

First and third class

A door

Second class

If the mechanical advantage is large, ____ effort is needed to accomplish work.

Less

What are the two basic equations for MA? MA = resistance force / effort force MA = effort distance / resistance distance

How would you increase the mechanical advantage of a wedge?

Make it longer and thinner

How would you increase the mechanical advantage of a screw?

Design the threads closer together

How would you increase the mechanical advantage of a wheel and axle?

The larger the wheel compared to the axle, the greater the MA.

The _______ the number of ropes supporting the resistance, the greater the MA.

greater

What are the two kinds of pulleys? Fixed and movable

All levers have two ______, called the ______ arm and the __________ arm.

Arms, effort, resistance

How do you calculate the MA for a lever? MA = effort arm / resistance arm