CH 14 .1

Work and Power

True False Statement True False

Work is the product of force, distance and time

Power is the amount of work done in a certain time

Horsepower, is compared to an actual horse’s power

The SI unit for work is the watt

The SI unit for power is the joule

Work

Work is the product of force and distanceForce is unbalanced

Requires Motion Depends on Direction

Some of the force must act in the same direction as the object moves

No movement = no work

Forces act in the same direction as the movement

Force that does not act in the direction of motion does not do work on an object

Work

Calculating Work

SI Units W= J, joule F = d = m

How much work is done by a weight lifter who lifts 1600N over his head, at a height of 2m?

Given:

Formula:

Solve:

Power

Power- rate of doing work

Work at a faster rate = increasing power

Increase power More work in a given

time More work in less time

Calculating Power

SI Units P= W, watt

= 1J per s W= J t= s

You exert a force of 72N to lift a box to a height of 1m in 2s. How much power is used to lift the box?

Give:

Formula:

Solve:

Math Practice pg 415

1.

3.

2.

Horsepower

Horsepower hp = 746 watts

James Watts Comparison of power

outputs of steam engines

vs output of strong horse

CH. 14 .2

Work and Machines

True False Statement True False

Machines make work easier, by changing force, direction or distance

The force you exert on a machine is output force

The final product of the machine is called output force

Output work is always less than input force due to friction

Both force input and force output are equal to force x distance

Machines and Work

Machine A device that changes force Make work easier by

Changing size of force Direction of force Distance over which force acts

Machines and Work

Increasing Force Small force over a

large distance = large force over a short distance

Ex-jack

Increasing Distance Decrease applied force

by increasing the distance in which the force is exerted

Changing Direction Ex-oar

Work Input

Input force- force you exert on

machineInput distance-

distance of input forceWork Input-

input force x input distance

Friction makes work done by a machine less than the work done on the machine

Work Output

Output force- force exerted by the

machineOutput distance-

distance of output force

Work Output- output force x output

distance

CH. 14 .3

Mechanical Advantage and Efficiency

True False Statement True False

Mechanical advantage is the # of times a machine increases output force

IMA is the ideal mechanical advantage, which is only possibly without friction

AMA is the actual mechanical advantage, which is output force/input

force

Efficiency of a machine is the input work that becomes output work

Efficiency can never equal 100%

Mechanical Advantage

The # of times that a machine increases an input force

Ex: Nut cracker At pivot- 7 times your input force At middle- 3 times your input force

Actual Ideal

IMA is the mechanical advantage in the absence of friction

Actual MA is always less than the IMA due to friction

Mechanical Advantage

•AMA is the actual forces acting on a machine

Calculating IMA

IMA = Input Distance Output

DistanceNo SI Unit

A woman drives her car onto a ramp for repairs. She drives 1.8m along the ramp to raise the car 0.3m. What is the IMA?

Given:

Formula:

Solve:

Math Practice pg 425

1.

3.

2.

Efficiency

The % of work input that becomes work output

Due to friction, it is always less than 100%

Efficiency= Work Output

Work Input

X 100%

Reduce friction = more efficiency

CH 14 .4

Simple Machines

True False Statement True False

Compound machines contain 2 or more of the 6 simple machines

There are 4 classes of levers, that depend where the fulcrum is located

A thin wedge has a bigger IMA than a thick wedge

A wheel and axle, is composed of 1 wheel, or disk

An inclined plane IMA is the height/ the distance

Simple Machines

6 Simple Machines

Lever

A ridged bar, free to move around a fixed point

Fixed point moves around a fulcrum

IMA = input arm/output arm

1st Class MA = 1, < 1, > 1

2nd Class MA = > 1

3rd Class MA = < 1

Name the Lever

Wheel and Axle

2 disks with different radiiIMA = radius of input force/ radius of output

forceMA = > 1

Inclined Plane

Slanted surface along which a force moves an object to difference elevation

IMA = distance of inclined plane/ change in height

Wedge

V shape, with 2 inclined planes sloped into each other

MA = > 1

Thin wedge of a given length has a greater IMA than a thick wedge of the same length

Screw

Inclined plane wrapped around a cylinder

Closer threads have more IMA than far apart threads

Pulley

Rope that fits into a groove in a wheel

IMA = # of rope sections supporting the load being lifted

Fixed Pulley Rotate in place MA = 1

Movable Pulley Attached to the object

being moved

Pulley System Mix of fixed and

movable

Name the Pulley

Compound Machines

Combination of 2 or more simple machines working together

Scissors Wedge, and lever

Name the simple Machines

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