Review from textbook, pages F68-F89
VOCABULARY
| efficiency | How well a machine changes effort into useful work | |
| effort force | The force put on one part of a simple machine, for example, when you push or pull on a lever | |
| fulcrum | The fixed point, or point that doesn't move, on a lever | |
| inclined plane | A flat surface with one end higher than the other | |
| lever | A simple machine made up of a bar that turns on a fixed point | |
| pulley | A simple machine made up of a rope or chain and a wheel around which the rope or chain fits | |
| screw | An inclined plane wrapped around a pole | |
| simple machine | One of the basic machines that make up other machines | |
| wedge |
A machine made up of two inclined planes placed back-to-back | |
| wheel and axle | A simple machine made up of a large wheel attached to a smaller wheel or rod | |
| work | That which is done on an object when a force moves the object through a distance |
CRITICAL THINKING
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
Simple Machines: An Introduction
Dirtmeister's Science Reporter's: Simple Machines