May The Force Be With You
Year 7 Science
Mr. Isgro
Checkpoint 1
What is a Force?
• Push
• Pull
• Twist (a combined push and pull)
Checkpoint 2
The application of a force may result in a change
in:
• Speed of an object
• Direction of an object
• Shape of an object
Checkpoint 2
A Force diagram A force diagram is usually used to
show the forces acting on an object. An arrow, with
a name, length and direction is used to represent a
force.
In a force diagram, the longer the arrow, the bigger
the force.
Checkpoint 3
Sir Isaac Newton:
Sir Isaac Newton, (December 25, 1642 - March 20,
1727) was an English alchemist, mathematician,
scientist and philosopher; who published the
“Philosophiae Naturalis Principia Mathematica (1687)”,
where he described universal gravitation and, via his
laws of motion, laid the groundwork for classical
mechanics.
Checkpoint 3
Sir Isaac Newton:
Newton’s contribution to our understanding of
forces and motion:
• Newton’s 1st Law of Motion
- Every object persists in its state of rest, or
uniform motion (in a straight line); unless, it is
compelled to change that state, by forces
impressed on it.
- A body remains at rest, or moves in a straight line
(at a constant velocity), unless acted upon by a
net outside force.
Checkpoint 3
Sir Isaac Newton:
• Newton’s 2nd Law of Motion
- Force is equal to the change in momentum
per change in time.
- The acceleration of an object is proportional
to the force acting upon it.
Checkpoint 3
Sir Isaac Newton:
• Newton’s 3rd Law of Motion
- Whenever one body exerts force upon a
second body, the second body exerts an equal
and opposite force upon the first body.
- For every action, there is an equal and
opposite reaction.
- Forces always come in equal pairs.
Checkpoint 3
Balanced forces Balance forces are two forces acting in
opposite directions on an object, and equal in size.
Anytime there is a balanced force on an abject, the
object stays still or continues moving continues to move
at the same speed and in the same direction.
Checkpoint 3
Unbalanced forces
• Unlike balanced forces, we say unbalanced forces
when two forces acting on an object are not equal in
size.
• Unbalanced forces causes can cause:
- a still object to move
- a moving object to speed up or slow down
- a moving object to stop
- a moving object to change direction
Checkpoint 3
Unbalanced forces
Notice that because there is a bigger force and a smaller
force involved, the direction of the wagon will be determined
by the bigger force. The wagon is moving as a result of
unbalanced forces.
Checkpoint 4
The Newton (N):
• Forces can be measured using a device called
force meter.
• The unit of force is called the newton. It is
represented by the symbol N.
• Force is measured in the unit call the Newton
(N).
• 1N=100g
Checkpoint 4
The Force Meter:
Force meters contain a spring
connected to a metal hook.
The spring stretches when a
force is applied to the hook.
The bigger the force applied,
the longer the spring
stretches and the bigger the
reading.
Checkpoint 5
Practical Activity:
• Measuring forces using rubber bands
Checkpoint 6
Types of forces:
• A force usually results from an interaction. The
interaction can be a physical one, or a non-physical
one.
• Forces resulting from physical interaction are called
'Contact Forces' and examples include Frictional,
Tension, Air resistance and Spring force.
• A force resulting from non-physical interaction is called
'Field force’ (or Action-at-a-distance force) and
examples include gravitational, electrical or magnetic
force.
Checkpoint 7
Frictional forces
• Friction is a contact force that stops (opposes)
things from moving easily.
• Whenever an object moves or rubs against
another object, it feels frictional forces. These
forces act in the opposite direction to the
movement.
• Friction makes it harder for things to move.
Checkpoint 7
Frictional forces
• Friction makes it harder for things to move.
• Without frictional forces, a moving object may
continue moving for a longer period.
• Frictional forces are usually greater on rough
surfaces (B) than on smooth surfaces (A).
Checkpoint 7
• Friction is a contact force that opposes motion.
• Everyday situations where friction acts:
- A basketball star can grip a ball and control it better in
a dunk because of greater friction.
- When we walk, we don’t slip easily because of the
friction between our shoes and the floor.
- Each time you ride your bike, friction between the
tires and the road help you not to skid off.
- Can you think of any other examples?
Checkpoint 7
Air resistance
• Moving objects like aircrafts, cars and arrows
experience air resistance when they are in motion.
• Frictional forces of the air against the moving object
cause this resistance.
• There is more (bigger) resistance with faster
movement, and less resistance with slower
resistance.
Checkpoint 7
Moments
• Moments is a scientific name for turning forces around a
pivot. Forces can make objects turn if there is a pivot.
• A see-saw will balance if the moments on each side of the
pivot are equal. This is why you might have to adjust your
position on a see-saw if you are a different weight from the
person on the other end.
Checkpoint 8
Gravitational Force
• This is an example of a
field force.
• Mass in NOT the same
as weight.
• Notice how the mass of
an astronaut remains
the same, whiles his
weight is smaller in
moon as a result of less
gravity.
Checkpoint 8
Gravitational Force
• Weight is determined by how much
something is pulled by gravity.
• Objects with more matter (mass) will weigh
more when pulled by the same gravitational
force (e.g. on Earth). Mass is measured in
kilograms, kg, or grams, g.
Checkpoint 8
Gravitational Force
• Gravitational force increases when the masses
are bigger and closer. This means that the
gravitational force on Moon is less than on
earth, because Moon has less mass than
Earth.
Checkpoint 8
Magnetic Force
• This is an example of a field force.
Checkpoint 9
Characteristics of a magnet
• Magnets have poles
(North and South poles)
• Like poles (N and N or S
and S) repel.
• Opposite poles (N and S)
attract.
Checkpoint 10
More on magnets:
• Magnets and compasses can be used to find
North.
- a temporary magnet can be used to make a
compass (refer to practical).
Checkpoint 10
More on magnets: Compass and Earth’s
magnetic poles
Checkpoint 11
• Draw field lines for magnets
Checkpoint 12
• Everyday situations where magnets and
electromagnets are used:
Magnets
Electromagnets
Fridge
Doorbell
Shower
Electric gates
Checkpoint 13
Practical Activity: Create an electromagnet
Checkpoint 13
Practical Activity: Create an electromagnet
• An electromagnet is a type of magnet in which
the magnetic field is produced by electric
current. The magnetic field disappears when
the current is turned off. Electromagnets
usually consist of a large number of closely
spaced turns of wire that create the magnetic
field.
Checkpoint 13
Practical Activity: Create an electromagnet
Checkpoint 14
• Energy is defined as the ability to do work.
• Work is defined as the transfer of energy.
• Energy is measured in Joules (J)
Checkpoint 15
Identify types of energy:
• Heat
• Light
• Sound
Checkpoint 15
Identify types of energy:
• Electrical
• Wind
• Nuclear
Checkpoint 15
Identify types of energy:
• Chemical
• Gravitational potential
• Kinetic
Checkpoint 16
Practical Activity:
• Comparing yellow and blue Bunsen burner
flames
Checkpoint 17
Uses of heating and energy in the home:
• Heater
• Air conditioner/Ceiling Fan
• Refrigerator
• Lighting
• Washing machine/Drier
• Dishwasher
• Pool pump
• Entertainment (TV, Radio)
• Computer
• Oven/Stove
Can you think of any more?
Checkpoint 18
Kinetic energy:
All moving things have kinetic energy. It is energy
possessed by an object due to its' motion or movement.
These include very large things, like planets, and very
small ones, like atoms. The heavier a thing is, and the
faster it moves, the more kinetic energy it has.
• Cars
• Trucks
• Trains
• Boats
Checkpoint 19
Gravitation potential energy:
• Every object may have Potential energy but
Gravitational energy is only stored in the
height of the object. Any time that a heavy
object is kept high up, a force or power is
likely to be holding it up there. This is the
reason why it stays up and does not fall. It is
important to note that the heavier the object,
the more its potential energy.
Checkpoint 20
Energy transformations: Chemical potential energy to
electrical energy
• Coal is a combustible black or brownish-black
sedimentary rock composed mostly of carbon and
hydrocarbons. Coal is made of the remains of
ancient trees and plants that grew in great swampy
jungles in warm, moist climates hundreds of millions
of years ago.
Checkpoint 20
Energy transformations: Chemical potential energy to electrical energy
1. Coal is milled to a fine powder, allowing it to burn more quickly. It is
blown into the combustion chamber of a boiler where it is burnt at high
temperature. 2. The hot gases and heat energy produced converts
water in tubes lining the boiler into steam. 3. The high-pressure steam is
passed into a turbine containing thousands of propeller-like blades. The
steam pushes these blades causing the turbine shaft to rotate at high
speed. The steam is condensed and returned to the boiling chamber
where it is heated again. 4. The shaft rotation engages the wire coils and
magnets in a generator connected to it. This charged magnetic field
produces electricity. 5. Electricity is sent to the switchboard
(transformer) where it is regulated and sent via on-land cables to homes.
Checkpoint 20
Energy transformations: Chemical potential energy to
electrical energy
http://www.eschooltoday.com/energy/kinds-of-energy/example-of-chemicalenergy.html
Checkpoint 20
Energy transformations: Chemical potential energy to
electrical energy
Also known as fuel, chemicals that are transformed into
another form of energy include:
- Coal
- Crude oil (a non-renewable resource)
- Natural gas (methane)
- Petroleum (crude oil)
- Biofuel (e.g. biodiesel, ethanol and hydrogen)
- Uranium (Nuclear)
Checkpoint 20
Energy transformations: Chemical potential energy to electrical energy
Below is a summary of the process that turns crude oil into electricity:
1.
2.
3.
4.
Oil is burnt in turbines in power stations to produce extreme heat,
which is used to create high-pressure steam. This steam is used to
spin a turbine very fast by pushing against metal blades.
The blades turn a generator containing wires and magnets and
magnetic field produces electricity.
The electricity flows to a transformer, which changes it to very
high voltage electricity. The transformer also regulates the
amount of electricity that is produced and supplied.
Electricity is sent to homes, factories and other places in the
world.
Checkpoint 20
Energy transformations: Chemical potential
energy to electrical energy
• Nuclear energy is energy in the nucleus (core)
of an atom. Atoms are tiny particles that make
up every object in the universe. There is
enormous energy in the bonds that hold
atoms together.
• Energy from uranium is called nuclear energy.
Checkpoint 20
Energy transformations: Chemical potential energy to
electrical energy
• Power generated from nuclear reaction is similar to
that of fossil fuels because they all use heat to turn
blades (turbines) to generate power.
Checkpoint 20
• What is Uranium (Nuclear Energy)?
• A nuclear power plant uses uranium as fuel.
Uranium pallets are combined into large fuel
assemblies and placed in a reactor core.
• In that chamber (reactor), uranium atoms can be
made to split, or fission, to release heat. 'Fission'
is the process of splitting the uranium atom to
form smaller atoms (1kg of natural uranium
produces as much heat as 20,000kg of coal). This
is harnessed to make steam and generate power.
Checkpoint 20
Energy transformations: Chemical potential energy to
heat energy
• Chemical Energy is energy stored in the bonds of
chemical compounds (atoms and molecules). It is
released in a chemical reaction, often producing heat
as a by product (exothermic reaction).
• Usually, once chemical energy is released from a
substance, that substance is transformed into an
entirely new substance.
• For example, when an explosive goes off, chemical
energy stored in it is transferred to the surroundings as
thermal energy, sound energy and kinetic energy.
Checkpoint 20
Energy transformations: Chemical potential energy to heat energy
• Batteries, biomass, petroleum, natural gas, and coal are
examples of stored chemical energy. Food is also a good example
of stored chemical energy.
Checkpoint 20
Energy transformations: Gravitational potential energy to kinetic
energy
• The gravitational energy of an object moving downwards, the
lower the kinetic energy, and the lower the kinetic energy of
an object moving upwards, the higher its gravitational energy.
Checkpoint 21
The Law of Conservation of Energy states that:
• energy cannot be created or destroyed, just
transformed from one form to another. These
forms can include kinetic and potential energy as
well as light, heat and sound. Energy can also be
transferred between objects. Since energy cannot
be created or destroyed, the amount of energy
present in the universe is always the same. It is
simply being transformed and transferred over
and over again.
Checkpoint 22
Methods of generating electricity:
1. Rotating turbines attached to electrical generators
produce most commercially available electricity.
2. Turbines are usually rotated using using steam (coal
is used to heat water), flowing water (hydro) or
wind.
3. Steam turbines can be powered using steam
produced from burning solid fossil fuels (e.g. coal,
gas, diesel, etc…), or using alternatives such as
geothermal sources or solar energy.
Checkpoint 22
Energy transformations in coal producing electricity:
View Clip - http://www.eschooltoday.com/energy/kinds-of-energy/example-of-chemical-energy.html
Checkpoint 22
Energy transformations in hydro producing electricity
• Hydroelectric power plants use water flowing directly
through the turbines to power the generators.
Checkpoint 22
Energy transformations in hydro producing electricity
1.
2.
3.
4.
The Dam is built to retain the water. More electricity is produced if
the water is more in the reservoir
Sluice Gates: These can open and close to regulate the amount of
water that is released into the pipes.
Potential energy in the retained water is transferred into kinetic
energy by water flowing through the pipes with high speed.
The force and high pressure in the water turns a series of shafts in
a generator. Spinning shafts in the generator charges millions of
coils and magnets to create electricity, which is regulated by a
transformer. This is then transported via cables to homes and
factories
Checkpoint 22
Energy transformations in hydro producing electricity
Checkpoint 22
Energy transformations in hydro producing electricity
Checkpoint 22
Energy transformations in wind producing electricity
• Wind generators use wind to turn turbines that are
hooked up to a generator.
Checkpoint 23
Efficiency of energy conversions:
• An arrow is used to show energy transfer. Energy is lost to the
surroundings at each transformation.
• Such conversions are inefficient as heat energy is lost at each
transformation
Checkpoint 24
Energy Conservation:
Saving energy can be achieved in a couple of
ways:
1.Energy conservation,
2.Energy Efficiency, and
3.Recycling.
These first two are not the same, even though
people often use them to mean the same thing.
Checkpoint 24
Energy Conservation:
• This is the practice that results in less energy being used. For
example, turning the taps, computers, lights, and TV off when not in
use.
• It also includes running in the park or outside instead of running on
the treadmill in the gym.
• Energy conservation is great because we can all do this everywhere
and anytime. It is a great behavior we must acquire. Did you
know: 1. Up to 25% of heat loss is through windows, plastic
window covers can help reduce drafts. 2. 85 to 90% of energy used
to wash clothes goes to heating water
Checkpoint 24
Energy Efficiency
• This is the use of manufacturing techniques and technology
to produce things that use less energy for the same result.
• For example if a heater is designed to warm your home
with less energy than regular heaters, that would be an
energy efficient heater.
• If your washing machine uses less energy to do the same
job as other washers, that is an energy efficient washer.
FACT: Homes built after 2000 are about 30% bigger, but there
use less energy than older homes.
Checkpoint 24
Recycling
• This involves the use of waste or old materials to make
new ones.
• For example, we can collect all old newspapers from
the town at the end of everyday and turn the papers
into fresh paper for printing again.
• Recycling saves energy because less energy is used to
recycle than to turn new raw materials into new
products.
• This means to save energy, we need to use all these
great ways. If we all try do this, together we can save
some money and use less natural resources too.
Checkpoint 24
Implications for society and the environment of
some solutions to increase the efficiency of
energy conversions:
• High costs