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.

For work to occur, an object must ____

move

The motion of the object must be in the ___ ___ as the applied force on the object.

same direction

Work and energy are related, since energy is always ____ from the object doing the work to the object on which the work is done.

away

Work is done on an object only when a ____ is being applied to the object and the object moves.

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.

Power is measured in _____

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

same amount of work can be done by applying a small force over a long distance as can be done applying a large force over a short distance, since work equals _____ times _____.

distance, force

increasing _____ reduces the amount of force needed to do the work.

distance

some machines change the _____ of the applied force to do the work.

force

machines help move things that _____ being moved.

resist

Force applied to machines is_____ _____

effort force

Resistance Force

force applied by machine to overcome resistance.

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

More

Some energy transferred is changed to _____ due to friction

force

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

friction

Mechanical advantage (MA)

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%.

Efficiency of a machine is always _____ than 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.

IMA of a Wheel and Axle

radius of wheel divided by the radius of axle

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)

Less force is required if a ramp is ____ and ____ steep

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.

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