Work and Machines

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If you exert a force of 20 newtons to push a desk 10 meters, how much work do you do on the desk?

200 joules

wedge

A device that is thick at one end and tapers to a thin edge at the other end.

machine

A device that makes work easier

watt

A measure of power equal to one joule of work per second.

lever

A rigid bar that is free to move around a fixed point

pulley

A simple machine that consists of a rope that fits into a groove in a wheel

wheel and axle

A simple machine that consists of two attached circular or cylindrical objects that rotate about a common axis, each one with a different radius.

screw

A simple machine that is an inclined plane wrapped around a central cylinder to form a spiral

joule

A unit of work equal to one newton-meter

The ideal mechanical advantage of a wheel and axle is the radius of the wheel times the radius of the axle.

False, radius of wheel divided by radius of the axle

A wheel and axle is a compound machine.

False, simple

In machine 2, which letter represents the input force?

In machine 2, G represents the input force.

In what class of lever is the direction of the input force opposite to the direction of the output force?

In the first class lever

Why is it more difficult to steer a bike when your hands are close together on the handlebars than when they are far apart?

It is more difficult because of where the fulcrum is located.

Explain how the ideal mechanical advantage and efficiency of a machine determine the machine's actual mechanical advantage.

It is often related to the measurements of a machine. What have you calculated so far (output force divided by input force) is actual mechanical advantage. If you know input work and the output work for a machine you can calculate a machine's efficiency.

How can a hockey stick be considered a machine?

It multiplies distance

Is machine 1 classified as a simple or a compound machine?

Machine 1 is classified as a simple machine.

Which machines multiply the input force?

Machines 4 and 5.

To which class of lever does each of the following machines belong: (i) fishing pole; (ii) wheelbarrow; (iii) bottle opener; (iv) pliers?

The i belongs to third class levers, the ii belongs to the second class lever, the iii belongs to second class levers, the iv belongs to first class levers.

The output force of a lever with an ideal mechanical advantage of 3 is used as the input force of a pulley system with an ideal mechanical advantage of 2. What is the ideal mechanical advantage of the compound machine? Explain.

The ideal mechanical advantage is 6. You take the input force and multiply it by the output force.

efficiency

The percentage of the input work that is converted to output work

Explain why wedges and screws are actually types of inclined planes.

The threads on a screw act like an inclined plane to increase the distance over which you exert the input force. When you use a wedge, instead of moving an object, you move the inclined plane itself.

A bricklayer lifts a stack of bricks onto his shoulder, carries it across a room, and then lifts the bricks onto a ledge above his head.Explain if work is being done in each of these three situations.

Work is being done to the bricks.

inclined plane

a flat, sloped surface

compound machine

a machine made of more than one simple machine

work

any time you exert a force on an object that causes the object to move some distance

One of the simple machines that turns is the wheel and

axle

One example of a compound machine is a

bicycle

A single fixed pulley changes the of a force.

direction

A machine makes work easier by multiplying force or , or by changing direction.

distance

Machines are devices that allow you to in an easier way.

do work

Divide output work by input work and multiply by 100% to find a machine's

efficiency

A knife is an example of a lever.

false

A machine's mechanical advantage is the output force multiplied by the input force.

false

If a compound machine is made of a pulley with a mechanical advantage of 3 and a wheel and axle with a mechanical advantage of 5, the mechanical advantage of the compound machine is 8.

false

If a machine changes the direction, but not the amount of the input force, the mechanical advantage is greater than 1.

false

If the machine increases distance, the output force is greater than the input force.

false

If you lift a box from the floor to a height of 1 m and then carry the box for 10 m, you do work only when you carry the box.

false

If you pull at an angle instead of in the direction in which the object moves, more of your force does work.

false

The ideal mechanical advantage of an inclined plane is the length of the plane divided by its force.

false

The lower arm acts like a first-class lever when it bends at the elbow.

false

The more power you use to move an object, the more work you do.

false

The part of a wheel and axle with the smaller radius is the wheel.

false

The thicker the wedge, the greater its mechanical advantage.

false

To find the mechanical advantage of a wheel and axle, multiply the radius of the wheel by the radius of the axle.

false

Joule is the rate at which work is done.

false, the amount of work done

fulcrum

fixed point on a lever

If tight scissors have an efficiency of 50 percent, half of your work is wasted due to

friction

The fixed point that a lever pivots around is the

fulcrum

The ideal mechanical advantage for an inclined plane is equal to the length of the incline divided by the

height of the incline

A flat, sloped surface is called a(n)

inclined plane

A ramp in a parking garage is an example of a simple machine called a(n)

inclined plane

The threads of a screw act like a(n)

inclined plane

The force you exert when you use a machine is the

input force

The unit of work is the

joule

A system of fixed and pulleys is called a block and tackle.

movable

simple machine

one of the six basic types of machines, which are the basis for all other forms of machines

In a compound machine, the of one simple machine becomes the input force of another simple machine.

output force

The force exerted by the machine is the

output force

Work divided by time equals

power

The wedge, screw, and lever are all

simple machines

power

the amount of work done per unit of time

output force

the force exerted on an object by a machine

The mechanical advantage of a machine is the number of times a machine increases

the force exerted on the machine.

input force

the force you exert on a machine

mechanical advantage

the number of times a machine increases a force exerted on it

For work to be done on an object,

the object must move some distance as a result of a force.

A bicycle is a compound machine because it contains more than one simple machine.

true

An ideal machine has no friction.

true

If the output force is greater than the input force, the mechanical advantage of the machine is greater than one.

true

In a first-class lever, the fulcrum is between the input force and the output force.

true

Power is the rate at which work is done.

true

The farther you move an object, the more work you do.

true

The force exerted by a machine is called the output force.

true

To find the mechanical advantage of a pulley, count the sections of rope that support the object.

true

When you use a wedge, instead of moving an object along the inclined plane, you move the inclined plane itself.

true

Work is done on an object when the object moves in the same direction in which the force is applied.

true

You do work on an object when you lift it off the floor onto a shelf.

true

A device that is twice as powerful as another can do the amount of work in the same amount of time.

twice

The unit of power is the

watt

Power is measured in units called

watts

A device that is thick at one end and thin at the other end is a

wedge

A simple machine that might be thought of as an inclined plane that moves is a

wedge

A screwdriver and a doorknob are examples of a(n)

wheel and axle

A screwdriver is a simple machine called a(n)

wheel and axle

Force multiplied by distance equals

work

Power is equal to divided by time.

work

The force you exert on an object multiplied by the distance the object moves is equal to , which is expressed in joules.

work


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