# Physical Science Chapter 5

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Physical science - work and machines

### Work

the transfer of energy that occurs when a force makes an object move.

move

same direction

away

force

### How do you calculate work?

work equals force (in newtons) times distance

### Power

Is the amount of work done in a certain amount of time; rate at which work is done.

### How do you calculate power?

power equals work/energy divided by time.

Watts W

### Since work and energy are _____, power also can be calculated.

related, power equals energy divided by time.

### Machine

A device that makes doing work easier.

### Machines _____ applied force and/or _____ direction of applied force to make work easier.

increase, increase

distance, force

distance

force

resist

effort force

### Resistance Force

force applied by machine to overcome resistance.

More

force

### An ideal machine with no _____ would have the same input work and output work.

friction

is the number of times a machine multiplies the effort force. It is calculated by MA equals resistance force divided by effort force.

### Efficiency

Measure of how much of the work put into a machine is changed into useful output work by the machine.

### How to calculate efficiency

efficiency equals (output work divided by input work) times 100%.

less

### Lubricant

Can make machines more efficient by reducing friction.

### Simple machine

A machine that does work with only one movement.

### Lever

A bar that is free to pivot about a fixed point called the fulcrum

### Effort arm of a lever

part of the lever on which effort force is applied

### resistance arm of a lever

is part of the lever that exerts the resistance force.

### Three classes of levers based on positions of ____ ____, ____ ____, ____

effort force, resistance force and fulcrum

### First class lever

fulcrum is located between the effort and resistance forces; multiplies and changes direction of force (screw driver).

### Second class lever

resistance force is located between the effort force and fulcrum always multiplies force (wheel barrel)

### Third class lever

effort force is between the resistance force and fulcrum; doesn't multiply force but does increase distance over which force is applied (baseball bat)

### Calculating ideal mechanical advantage (IMA) of a lever

IMA equals length of effort arm divided by length of resistance arm.

### Pulley

A grooved wheel with a rope, simple chain, or cable running along the groove. A modified first-class lever.

### A fixed pulley

Attached to something that doesn't move; force is not multiplied but direction is changed; IMA = 1

### A moveable pulley

has one end of the rope fixed and the wheel free to move; multiplies force; IMA = 2.

### Block tackle system of pulleys

consisting of fixed and moveable pullleys; IMA = number of ropes supporting resistance weight.

### Wheel and Axle

machine with two wheels of different sized rotating together modified lever form.

### gears

modified form of the wheel and axle

### Inclined Plane

sloping surface that reduces the amount of force required to do work.

### IMA of Inclined Plance

length of slope (effort distance) divided by height of slope (resistance distance)

longer and less

### Screw

An inclined plane wrapped in a spiral around a cylindrical post.

### Wedge

An inclined plane with one or two sloping sides.

### Compound Machines

Uses a combination of two or more simple machines.

Example: