Jillian Pardini & Hank Finch Work and Machines Jillian Pardini & Hank Finch

Machines A machine is a device that changes a force and makes work easier to do. Machines change the size of a force needed, the direction of a force, or the distance over which a force acts. Machines make things easier by accomplishing one or more of the following; Transferring a force from one place to another Changing direction of a force Increasing the magnitude of a force Increasing the distance or the speed of the force

Simple machine examples Inclined plane Screw Pulley Wheel and Axle Wedge Lever

Increasing Force If a machine increases the distance in which you exert a force, then it decreases the amount of force needed to exert. Lifting something one at a time takes less force but you travel a greater distance.

Increasing Distance A machine that increases the distance in which you exert a force increases the amount of force required. To row a boat you pull the oar a short distance to move the other end a large distance. This in turn requires you to exert a greater force.

Work Input & Output Work Input Work Output Input force is the force you exert on a machine. The distance a force travels is input distance. The work done on the input and travels through the input distance is work input. Work input force equals the input force multiplied by the input distance. The force that is exerted by a machine is called the output force. The distance the output is exerted through is the output distance. All machines use some amount of input work to overcome friction.

Friction When rowing a boat work is done on the oar which in turn do work on the water to move the boat. As rowers pull in one end of each oar the other end pushes against the water. The force of the oar in the water causes an equal and opposite reaction force to be exerted by the water on the oar. Although due to friction, the work done by the machine is always less than the work done on the machine so you can never get more work out than you put in.

Quiz Time

1. When a machine does work on an object the output work is… Always less than the input work Always equal to the input work Always greater than the input work Sometimes equal to the input work

2. A machine can do any of the following except… Increase distance Increase work Increase force Change direction

3. The force that causes objects to slow down or stop is… Work Force Friction Direction

4. A inclined plane is an example of… Increasing force Increasing distance Changing direction Friction

Resistance Power Effort Work 5. The transfer of energy that occurs when a force makes an object move… Resistance Power Effort Work

6.The rate at which work is done… Force Efficiency Power Effort

7. Simple machines make work easier by trading ________ for force. Distance Motion Friction Work

8. How does a ramp make lifting a heavy object easier? The object is moved over a shorter distance The ramp increases the amount of work you do Less force is needed to move the object over a longer distance More force is needed to move the object over a longer distance

Give an example of a simple machine and what it could be used for. Extra Credit: Give an example of a simple machine and what it could be used for.

Answers A B C D