Making work easier

The idea

Simple machines are devices that make a task easier by changing the magnitude or direction of the force to be applied, though the total work required cannot be reduced.

A heavy box on a platform

A heavy box has to go up onto a platform. You can lift it, push it up a plank, or use a rope over a wheel.

What do you think these helpers change about the job?

• How hard we must push or pull, or in which direction
• The total work needed, which becomes zero
• The mass of the box

What does each change?

Sort each machine by what it changes about the force.

Easier, not less work

A machine can change how big the force is, or which way it points. It cannot reduce the total work needed for the task. The pulley, the inclined plane and the lever are the three simple machines we study.

Simple machines are devices that make a task easier by changing the magnitude or direction of the force to be applied, though the total work required cannot be reduced.

Notes

A simple machine changes the magnitude or direction of the force to make a task easier; the total work cannot be reduced.

Check yourself

A simple machine can change…

A flag is raised by pulling a rope downward over a fixed pulley. What does the pulley change?

Which three simple machines does the book study?

Can a simple machine reduce the total work required for a task?

• the total work needed for the task into zero. The total work required cannot be reduced. The machine changes the force, not the total work.
• the mass of the load. The machine does not change the mass of the load. It changes the force to be applied.
• the magnitude or the direction of the force we apply — correct. Yes!
• The direction of the force — correct. Yes!
• The total work, which becomes smaller. The total work cannot be reduced by a machine.
• The magnitude of the force, which becomes smaller. A fixed pulley does not reduce the magnitude. It changes only the direction.
• The pulley, the spring and the pendulum. The spring and the pendulum are not the simple machines studied here.
• The pulley, the inclined plane and the lever — correct. Yes!
• The inclined plane, the thermometer and the lever. A thermometer is an instrument, not one of the simple machines studied here.
• Yes, it can reduce the total work to a small value. The total work required cannot be reduced.
• Yes, but only a lever can. No machine reduces the total work required.
• No, it only makes the task easier by changing the force — correct. Yes!