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- Energy is the ability to do
work.
Work is the use of a force to move an object
across a distance. The formula for work is:
work = force x
distance
A
force is any push or pull on an
object. Force is measured in units called
Newtons
(
N). It takes 1N to move a mass of 100g. The formula for
force is:
force = mass x accelerationWork
is measured in units called
Joules (
J). Using
our formula for work, we know that 1 Joule is equal to 1 Newton times 1 meter.
(1J = 1N x 1m)
Types of
Energy
Potential Energy - "Stored energy" or
"Energy of Position". This is energy that is stored by the object's position,
shape, or chemistry.
Kinetic Energy - "Energy
of Motion". This is the energy that an object has while it is
moving.
Chemical Energy - A type of potential energy
that is stored in chemicals (food, fuel, etc.) and is realeased by chemical
reactions.
For example, when you eat food, your body digests it to release
the energy stored in the food so that you can run and jump and skip and
play.The Law of Conservation of
Energy
Energy cannot be created or destroyed; it can only
change form.
Types of
Forces- Buoyancy - Force exerted when water
pushes an object to its surface. (i.e. - A ship's buoyancy causes it to
float.)
- Elastic Force - Exerted when an object wants to
return to its original shape. (i.e. - A stretched rubber band exerts an
elastic force, because it will snap back to its original
shape.)
- Friction - Force that opposes
motion.
- Gravity - The pull exerted by the
Earth.
- Magnetism - Force exerted by a magnet (attractive or
repulsive).
- Mechanical Force - A physical push/pull exerted
by an object. (i.e. - Throwing the ball is an example of a mechanical
force.)Pressure - Force created when a substance is
compressed. (i.e. - There is pressure at the bottom of the ocean from the
weight of all that water pushing down.)
Simple
Machines- Machine - A device that makes doing work easier.
- Simple Machine - One of six basic devices that change the size or direction of a force. Simple machines are divided into two categories:
- Inclined Planes - Sloping surfaces (such as a ramp).
- Inclined Plane
- Wedge
- Screw
- Levers - A bar that can pivot around a fixed point.
- Lever
- 1st Class - fulcrum in the middle (reduces input force, increases input distance - makes the work easier)
- 2nd Class - resistance in the middle (reduces input force, increases input distance - makes the work easier)
- 3rd Class - effort in the middle (reduces input distance, increases input force - makes the work faster)
- Pulley
- Wheel & Axle
We will be looking at four types of simple machines in
this unit: the inclined plane, lever, pulley, and wheel & axle. Students
will need to learn and be able to use the following formulas:
1 N
= 100 g 10 N = 1,000 g = 1
kg
Work = Force x Distance (J = N x
m)
Mechanical Advantage = Force
Output
Force
Input
Efficiency = Work
Output
Work
Input
Input is the force/work that you put into
a machine. It is the work you do to push on the lever or pull the string of the
pulley.
Output is the force/work that you get out of the
machine. It is the work that the machine does to move the
object.
Mechanical Advantage is a measure of how much
the machine multiplies your force. For example, if a machine has a mechanical
advantage of 3, this means that it will triple the force that you exert on it.
(If I push on the lever with 1N of force, the other end of the lever will push
on the object with 3N of force.) This number will generally be larger than
1.
Efficiency is a measure of how much work you get out
of a machine, compared to how much you put in. Efficiency is sometimes written
as a decimal, and sometimes as a percentage. As a general rule, it will always
be less than 100% (less than 1, if written as a decimal).
Resources
Crash Course Physics (Playlist)Feather & Hammer Drop on the Moon (0:47) An experiment by the Apollo 15 astronauts.
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