Physics Chapter 3: Work and Machines Flashcards

Questions and Answers

What is the formula for work?

Force x Distance (correct)

Distance / Time

Force + Distance

Force / Distance

What is power?

The rate at which work is done.

What is the SI unit of energy?

Joule

What is a watt?

A measure of power equal to one joule of work per second. Signup and view all the answers

Work divided by time equals what?

Power Signup and view all the answers

What is the unit of work?

Joule Signup and view all the answers

What is the unit of power?

Watt Signup and view all the answers

Force multiplied by distance equals what?

Work Signup and view all the answers

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

True Signup and view all the answers

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

False Signup and view all the answers

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

True Signup and view all the answers

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

False Signup and view all the answers

Power is the rate at which work is done.

True Signup and view all the answers

What is a machine?

A device that makes work easier. Signup and view all the answers

What is input force?

The force exerted on a machine. Signup and view all the answers

What is output force?

The force exerted on an object by a machine. Signup and view all the answers

What is mechanical advantage?

The number of times a machine increases a force exerted on it. Signup and view all the answers

What is efficiency?

The percentage of the input work that is converted to output work. Signup and view all the answers

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

do work Signup and view all the answers

The force you exert when you use a machine is the _________________

input force Signup and view all the answers

The force exerted by the machine is the _________________

output force Signup and view all the answers

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

work Signup and view all the answers

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

efficiency Signup and view all the answers

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

False Signup and view all the answers

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

True Signup and view all the answers

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

False Signup and view all the answers

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

False Signup and view all the answers

An ideal machine has no friction.

True Signup and view all the answers

What is an inclined plane?

A flat, sloped surface. Signup and view all the answers

What is a wedge?

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

What is a screw?

An inclined plane wrapped around a cylinder. Signup and view all the answers

What is a lever?

A rigid bar that is free to move around a fixed point. Signup and view all the answers

What is a fulcrum?

The fixed point around which a lever pivots. Signup and view all the answers

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

False Signup and view all the answers

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

True Signup and view all the answers

The thicker the wedge, the greater its mechanical advantage.

False Signup and view all the answers

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

True Signup and view all the answers

A knife is an example of a lever.

False Signup and view all the answers

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

False Signup and view all the answers

A flat sloped surface is called a(n) ____________________.

inclined plane Signup and view all the answers

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

wedge Signup and view all the answers

The threads of a screw act like a(n) ____________________.

inclined plane Signup and view all the answers

The fixed point that a lever pivots around is the ____________________.

fulcrum Signup and view all the answers

What is a pulley?

A simple machine that consists of a rope that fits into a groove in a wheel. Signup and view all the answers

What is a wheel and axle?

Two different sized circular objects that are attached together and turn as one. Signup and view all the answers

What is a compound machine?

A machine made of more than one simple machine. Signup and view all the answers

One of the simple machines that turns is the wheel and ______________.

axle Signup and view all the answers

A single fixed pulley changes the ____________________ of a force.

direction Signup and view all the answers

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

movable Signup and view all the answers

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

wheel and axle Signup and view all the answers

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

output Signup and view all the answers

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 Signup and view all the answers

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

False Signup and view all the answers

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

True Signup and view all the answers

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

True Signup and view all the answers

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

False Signup and view all the answers

For work to be done on an object, ____________________.

the object must move some distance as a result of a force Signup and view all the answers

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 Signup and view all the answers

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

the amount of friction Signup and view all the answers

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

Wedge Signup and view all the answers

Give an example of a compound machine.

Bicycle Signup and view all the answers

What is the ideal mechanical advantage for an inclined plane?

Equal to the length of the incline divided by the height of the incline. Signup and view all the answers

How can a hockey stick be considered a machine?

It multiplies distance. Signup and view all the answers

If tight scissors have an efficiency of 50 percent, what does that mean?

Half of your work is wasted due to input force. Signup and view all the answers

Power is measured in units called?

Watts Signup and view all the answers

The wedge, screw, and lever are all?

Simple machines Signup and view all the answers

What is a screwdriver?

A simple machine called a wheel and axle. Signup and view all the answers

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

twice Signup and view all the answers

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

distance Signup and view all the answers

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

Inclined plane Signup and view all the answers

Power is equal to ______ divided by time.

work Signup and view all the answers

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

True Signup and view all the answers

A wheel and axle is a compound machine.

False Signup and view all the answers

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

False Signup and view all the answers

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

False Signup and view all the answers

Joule is the rate at which work is done.

False Signup and view all the answers

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

It is classified as a simple machine because the only simple machine that is there is a pulley. Signup and view all the answers

In machine 2, which letter represents the input force?

The letter that represents the input force is G. Signup and view all the answers

Which machines multiply the input force?

Letter F Signup and view all the answers

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.

Yes because he is using a ledge which is a simple machine. Signup and view all the answers

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

100 because it is the ideal mechanical advantage so it determinants the actual M.A from 100. Signup and view all the answers

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

The first class levers Signup and view all the answers

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

A fishing pole is a third class lever, A wheelbarrow is a second class lever. A bottle opener is a second class lever. Pliers is second class. Signup and view all the answers

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

A wedge is a triangular shaped object, and is a portable inclined plane. It's one of six simple machines. Signup and view all the answers

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.

It would be 6 because 3 times 2 equals 6. Signup and view all the answers

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's harder to steer a bike when your hands are close together on the handlebar than when they are farther apart because that is just how things work. Signup and view all the answers

Study Notes

Work and Energy

Work is defined as force multiplied by distance; its unit of measurement is the joule (J).
Power is the rate at which work is done and is measured in watts (W), where 1 watt equals 1 joule per second.
The efficiency of a machine indicates the percentage of input work converted to output work.

Machines

A machine is a device that makes work easier by increasing force, distance, or changing the direction of force.
The force applied to a machine is called input force, while the force exerted by the machine is the output force.
Mechanical advantage is the factor by which a machine increases the input force, calculated as output force divided by input force.

Types of Simple Machines

Simple machines perform work with a single movement and include:
- Inclined Plane: A flat sloped surface that allows lifting objects more easily.
- Wedge: A device that tapers to a thin edge, facilitating splitting or lifting.
- Screw: An inclined plane wrapped around a cylinder.
- Lever: A rigid bar that moves around a fixed point known as the fulcrum.
- Pulley: A wheel with a groove that changes the direction of a force.
- Wheel and Axle: Comprises two circular objects that rotate together, aiding in movement.

Mechanical Advantage and Efficiency

The ideal mechanical advantage for an inclined plane is its length divided by the height of the incline.
In a compound machine, the output of one machine acts as the input for another, affecting overall efficiency.
The effectiveness of a machine can be impacted by factors like friction, with an ideal machine having no friction.

Working with Forces

Work is only done when an object moves in the same direction as the applied force, and this factor is crucial in calculating the work done on an object.
If multiple forces are applied, only the component of the force in the direction of motion does work.

True or False Statements

Work is done lifting an object if it moves; lifting is not the only condition to consider work done.
The rate of doing work (power) does not equate to doing more work but rather doing work faster.

Class of Levers

The configuration of forces in levers and their classes affect their functioning:
- First Class Lever: Fulcrum is between input and output forces (e.g., seesaw).
- Second Class Lever: Output force is between input force and fulcrum (e.g., wheelbarrow).
- Third Class Lever: Input force is between output force and fulcrum (e.g., fishing pole).

Practical Examples

A bicycle is classified as a compound machine due to its multiple simple machines.
A common application of a screw is its thread, acting as an inclined plane to convert rotational force to linear motion.

Working and Tools

Household tools like screwdrivers are simple machines designed to ease tasks by amplifying applied forces or altering motion direction.
Understanding the mechanics behind these machines allows for more efficient use in practical applications.

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Test your understanding of key concepts related to work and machines with these flashcards. Each card defines essential terms such as work, power, and the units of energy. Perfect for reviewing before your exam!