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Physical Science Chapter 5

Physical science - work and machines
STUDY
PLAY
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.