Levers, Pulleys
and
Simple Machines
and
Simple Machines
Science Study Guides
|
Levers, Pulleys
and Simple Machines |
|
Simple Machines
| energy | The ability to do work. | |
| work | When a force moves an object. | |
| force | A push or a pull. | |
| effort | The force applied to move a load using a simple machine. | |
| simple machine | Any of the six elementary devices that provide mechanical or other advantage. | |
| complex machine | A machine that is designed using a number of simple machines, often run by a motor. | |
| kinetic energy | The energy of motion. | |
| potential energy | Stored energy. |
Notes:
Name the six simple machines?
The six most common simple machines are the:
lever, pulley, inclined plane, wedge, screw, and wheel and axle.
Class 1, Class 2, and Class 3 Levers
| class-1 lever |
A lever in which the fulcrum is between the load and the effort. |
|
| load | The weight or resistance that is moved using a simple machine. | |
| lever arm | A beam, free to pivot around a point. | |
| fulcrum | The point at which a lever arm pivots. | |
| class--2 lever | A lever in which the load is between the fulcrum and the effort. | |
| bellows | A device that takes in air when the sides are spread apart and expels it through a tube when the sides are brought together. | |
| mechanical advantage | A ratio of the load or resistance to the effort or force. | |
| equal-arm balance | A scale used to compare masses placed at equal distances from the fulcrum. | |
| class-3 lever | A lever in which the effort is between the fulcrum and the load. | |
| catapult | A large class-3 lever system used in ancient times to launch heavy objects. |
The Wheel and Axle
| wheel and axle |
Two wheels of different diameters attached and rotating on the same axis. |
|
| windlass | A wheel and axle system used to apply force to a rope while winding it around the axle. A windlass can also be called a winch. |
The Inclined Plane
| inclined plane | A flat surface set at an angle, used to change the direction of a force. | |
| slope | The slant of an inclined plane. |
The Wedge
| wedge |
A double inclined plane that tapers to a point or sharp edge, used to change the direction of force. |
The Screw
| screw | An inclined plane spiraled around an axis. | |
| thread | A ridge or groove that spirals around a screw. |
Pulleys
| pulley | A wheel with a grooved rim in which a rope can run to change the direction of the pull and so lift a load. | |
| fixed pulley | A pulley attached in position above a load to be lifted. | |
| movable pulley | A pulley attached to a load that is being lifted. | |
| compound pulley | Two or more pulleys working together. | |
| sheave | A grooved wheel used in a pulley. | |
| block and tackle | Another name for a pulley system. | |
| chain hoist | A compound pulley system using chain instead of rope. | |
| hydraulic | Operated by means of fluid pressure. | |
| newton | The metric unit used to measure force. |
Questions For Study
1. Why is energy needed?
Energy is needed to do work.
2. How do scientists define “work”?
Work occurs when a force moves an object.
3. What kind of energy do both food and gasoline contain?
Food and gasoline both contain chemical energy.
4. Explain how one form of energy is changed to another form.
Electrical energy can be changed to light
energy and heat energy by light bulbs. Electrical energy can also be changed
into sound energy by a radio or audio device.
Chemical energy in gasoline can be used to make machines move. To do this, chemical
energy is burned to release heat energy. The heat energy is then changed to
mechanical energy.
Chemical energy storied in wood is changed to heat energy and light energy when
the wood is burned. Chemical energy is also stored in fireworks. When a firework
takes off and explodes the chemical energy produces movement (mechanical energy)
and the explosion produces sound, light, and heat energy.
5. What is the difference between kinetic and potential energy?
Kinetic energy is the energy of motion. The
kinetic energy of an object depends on its mass and speed. If you increase the
mass and/or the speed you increase the kinetic energy o an object.
Potential energy is stored energy.
6. How is a battery an example of both kinetic and potential energy?
A battery has chemical potential energy. The chemical energy is stored until
the battery is connected in a circuit. Then it is changed to electrical energy.
The electrical energy might be used to light a light bulb.
7. What is the difference between class 1, class 2, and class 3 levers?
A class-1 lever has the fulcrum located somewhere
between the effort and the load. With this kind of lever, the direction of force
is changes. Effort applied downward moves the load up. Effort applied upward
moves the load down.
A class-2 lever has its fulcrum at one end of a lever arm. The load is between the fulcrum and the effort. With this kind of lever, the direction of effort is not changed. Pushing up on the class-2 lever arm pushes up on the load. Pushing down on the lever arm pushes down on the load. To gain a mechanical advantage, the load is places closer to the fulcrum than to the effort. The class-2 lever always reduces effort.
In a class-3 lever, the fulcrum is at one end, and the effort is applied between the fulcrum and the load. With this kind of lever, the direction of effort is not changed. The load moves in the same direction as the effort. The gain offered by a class-3 lever is one of distance.
8. Explain why a simple machine makes work easier to do but does not save energy.
Most simple machines do not save energy.
They distribute the force needed to do work over a longer distance.
Generally, simple machines can help us in two ways. We can apply less effort
over a greater distance, or we can apply more effort over a shorter distance.
Simple machines provide a gain in effort or a gain in distance. In addition,
some simple machines change the direction of effort.
9. How does a lever or pulley give you mechanical advantage?
Sometimes we may want to lift, push, or pull
an objects, or we may need to break or cut them. Some of these jobs require
a lot of force. When we use simple machines, we gain a mechanical advantage
by increasing the amount of force we can bring to bear on an object.
10. What is friction? When is it necessary to reduce friction?
Friction is a force that slows down or stops
motion. There is friction when two parts of a machine rub against each other.
One way to reduce friction is by covering surfaces that rub together with grease
or oil. Another way is by using wheels.
11. What is the difference between a fixed and a movable pulley?
A fixed pulley can change the direction of
your force. You pull down on one end of the rope. The load is pulled up by the
other end. It takes the same force to lift a load with a fixed pulley as it
does without a fixed pulley.
A movable pulley does not change the direction of your force. Like a lever,
a movable pulley lets you use less force to lift a load. But you must pull the
rope a longer distance than the load moves. The smaller force needed to lift
a load with a movable pulley is used over a longer distance. So a movable pulley
does not save energy.
12. Where in real life can you find levers and pulleys?
Examples of class-1 levers are: a seesaw,
claw hammer, crowbar, scissors, pliers, and tin snips.
Examples of class-2 levers are: a wheelbarrow, paper cutter, door, nutcracker,
garlic press, bellows, and a bottle opener.
Examples of class-3 levers are: a fishing pole, hammer, baseball bat, hockey
stick, golf club, tennis racket, shovel, pitchfork, hoe, broom, tweezers, ice
tongs, and your arms and legs.
Pulleys are used to lift items from one level to another. Pulleys can be fixed
or movable or combinations of both. Pulleys are used in block and tackles, large
cranes, chain hoists, and hydraulic systems.
Websites for Energy and Simple Machines
Background Information on Simple Machines
Inquiry Almanac: Simple Machines
Motion, Energy, and Simple Machines
Dirtmeister's Science Reporter's: Simple Machines