chapter 12 work and machines. chapter 12 section 1 - what is work? work is done on an object when...
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Chapter 12 Work and Machines
Chapter 12
Section 1 - What is work?
Work is done on an object when the object moves in the same direction in which the force is exerted.
Work - The product of force and distance when a force is used to move an object.
No work without motion
Section 1 - What is work?
The amount of work done on an object can be determined by multiplying force times distance.
Work = Force x Distance work units - Joules (J)
Chapter 12
Section 1 - What is work?
Power is the rate at which work is done.Power equals the amount of work done
on an object in a unit of time.
Chapter 12
Time
WorkPower DistanceForceWork
Time
ForcePower
Distance
Section 1 - What is work?
Power = Joules/second = watt (W)kW = 1,000 W1 horsepower = 746 W
Chapter 12
Chapter 12
Section 2 -How Machines Do Work
Machine - A device that changes the amount of force exerted or
the direction in which force is exerted. A device with which you can do work in a way that
is easier or more effective.
A machine makes work easier by changing at least one of three factors. A machine may change the amount of force you exert, the distance over which you exert your force, or the direction in which you exert your force.
Chapter 12
Section 2 -How Machines Do Work
pg.415
Increase force, decrease distance
Increase distance, decrease force
Change direction
Section 2 -How Machines Do Work
A machine’s mechanical advantage is the number of times a machine increases a force exerted on it.
Chapter 12
ForceInput
ForceOutput (MA) Advantage Mechanical
Section 2 -How Machines Do Work
Friction reduces mechanical advantageThe efficiency of a machine compares the
output work to the input work.Efficiency is expressed as a percent.Efficiency = output work/input work x
100%Problems on page 418
Chapter 12
Chapter 12
Section 3 - Simple Machines
Six types of machinesInclined planeWedgeScrewLeverWheel & axlePulley
Chapter 12
Inclined Plane
An inclined plane is a flat sloped surface.Less force exerted over longer distance
Inclined Plane
You can determine the ideal mechanical advantage of an inclined plane by dividing the length of the incline by its height.
Ideal Mechanical Advantage= Length of incline/ Height of incline.
Chapter 12
Chapter 12
Wedge
A wedge is a device that is thick at one end and tapers to a thin edge at the other end.
Less force exerted over longer distance
Wedge
The ideal mechanical advantage of a wedge is determined by dividing the length of the wedge by its width.
Chapter 12
Chapter 12
Screw
Inclined plane wrapped around a cylinderLess force
Screw
The ideal mechanical advantage of a screw is the length around the threads divided by length of the screw.
Chapter 12
Chapter 12
Lever A lever is a rigid bar that is free to pivot, or rotate, on a fixed point. Fulcum - the fixed point that a lever pivots around
Lever
The ideal mechanical advantage of a lever is determined by dividing the distance from the fulcrum to the input force by the distance from the fulcrum to the output force.
Ideal mechanical advantage = Distance from fulcrum to input force / Distance from fulcrum to output force
Chapter 12
Chapter 12
3 Types of Levers
Wheel and Axle
A wheel and axle is a simple machine made of two circular or cylindrical objects fastened together that rotate about a common axis.
Chapter 12
Chapter 12
Wheel and Axle
Less force exerted over longer distanceDoorknob
Wheel and Axle
You can find the ideal mechanical advantage of a wheel and axle by dividing the radius of the wheel by the radius of the axle.
Mechanical advantage = Radius of wheel / Radius of axle
Chapter 12
Chapter 12
PulleyA pulley is made of a grooved wheel with rope or cable wrapped around it.Change amount and direction of input force
Pulley
The ideal mechanical advantage of a pulley is equal to the number of sections of rope that support the object.
Chapter 12
Chapter 12
Section 4 - Machines in the human body
Lifting levers - most of the machines in your body are levers that consist of bones and muscles.
Pg.432 Levers in the bodyWedges - front teeth (incisors)Break toothpick in fingers
Compound Machines
A compound machine is a machine that utilizes two or more simple machines.
The ideal mechanical advantage of a compound machine is the product of the individual ideal mechanical advantages of the simple machines that make it up.
Chapter 12
Chapter 12
Ch. 12 Vocabulary
work, machine, efficiency, mechanical
advantage, inclined plane,
wedge, screw, lever, fulcrum, wheel and axle, pulley