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CARSAnd Forces - Gravity
Non Contact ForcesNon Contact Forces
To be able to:
All Most Some
Say what is meant by gravity
(Level 4)
Give examples of forces that don’t need objects to touch
(level 5)
Explain the difference between mass and weight
(Level 6)
Starter – List all the things that a force could do to a ball
What happened
before Isaac Newton
invented gravity?
Why doesn’t water come out of
the tap sideways?
Why does rain always fall downwards
towards the Earth?
Why don’t people on the other side of the Earth
fall off into outer space?
Why did the ball fall down?
The answer to all these questions is the force called…
What is Gravity?What is Gravity?
Gravity is a force (gravitational force) that acts on all objects on earth.
This force holds the Earth (and the other planets) in orbit around the sun and the moon
around the Earth and satellites in orbit around the Earth.
The larger the mass of an object, the larger
the force of gravity.
Gravity- recapGravity- recapThe force of GRAVITY is
what keeps us on the SURFACE of the
EARTH.
You do not have to be TOUCHING the Earth
to feel the force of gravity.
GRAVITY ON EARTH PULLS YOU DOWN.
GRAVITY ALWAYS PULLS; IT NEVER
PUSHES.
We can draw an arrow on the shark and car to show the direction
of gravity:
Upwards Forces IUpwards Forces IIf there is a downwards force of gravity pulling
on a car then why does it not get pulled into
the ground?
There must be a force PUSHING UP on the car
that stops it getting pulled into the ground.
Gravity
Do you know what we call this force?
The REACTION FORCE.
Reaction
Upwards Forces IIUpwards Forces IIIf there is the downwards
force of gravity pulling down on a floating shark then why does it not sink
deeper into water?
There must be a force PUSHING UP on the
shark that stops it getting pulled further down. Gravity
Do you know what we call this force?
The UPTHRUST.
Upthrust
Force Diagrams exerciseForce Diagrams exerciseLabel the forces acting on a rocket moving through the Earth’s atmosphere.
Thrust
Air resistance
Gravity
Upthrust
Force Diagrams ExerciseForce Diagrams ExerciseLabel the forces acting on the shark.
Thrust Friction
Gravity
Upthrust
What could force do to a ball?What could force do to a ball?
•Remember, forces can be:•Push•Pull•Twist
Do things have to touch for forces to work?
Weight – What is weight? Weight – What is weight? The pulling force of gravity always acts towards the centre
of the Earth, wherever you are on the planet.
Why is weight different to mass?
Weight is a force and is measured in Newtons.Newtons.
The effect of the force of gravity on an object is called the object’s…
Mass – What is mass? Mass – What is mass? The amount of material in an object.
MASS is the resistance to a change in the motion of
a body.
Mass remains constant anywhere in the universe.
Weight does not remain constant anywhere in the universe.
The girl’s weight due to the force of gravity is
pulling her mass down on the chair.
An upwards force is produced by the chair
in the opposite direction to gravity.
The girl below is not moving. Are there any forces acting on her?
The girl does not move because these forces are balanced.
What does this tell you about the size of these forces?Draw five examples of balanced forces.
PracticalPractical• Hang a holder from the spring balance.
• Find a mass.• What is its mass in Kg (1000g = ??kg)
• Add it to the holder.• Read the weight on the spring balance.
• Record your results in a table.
Results sheet
ACTI VI TY I s there a relationship between weight and mass?
Mass (kg) Weight (N) Weight / Mass (N/kg)
Now draw a graph of your results
What happens to weight and mass when gravity changes?
Gravity changes depending on where you are in the Universe.
Our friendly alien Ms. A Lean will help you find out more…
On Earth, a mass of 1 kg has a weight
of 10 N.
My mass is 42 kg.
What is my weight on
Earth?
The force of gravity on the
Moon is 6 times less
than on Earth.
My mass is still 42 kg. What is my
weight on the Moon?
In outer space, far away from any planets or stars, there is
no gravity pulling on me.
My weight in outer space is
0 N. What is my
mass in outer space?
Testing our KnowledgeTesting our Knowledge
• Look at Concept Cartoon 11.7
• What do you think?
Gravity PoemGravity PoemWorking in pairs… write a 5-line poem about Gravity
Line 1 is one word – it’s the KEY ISSUE for today - GRAVITYLine 2 is two words and describes what the first line MEANSLine 3 is three words and describes what the first line DOESLine 4 is four words - say what the first line MEANS TO YOULine 5 is one word and says the first line using ANOTHER
WORD
Example DISSOLVINGbreak apartmakes pieces smallersolid mixes with liquidPHYSICAL
HomeworkHomeworkYou will explain what you have learned in these three lessons to someone at home.
Write down 5 bullet points to help you (I want to see those bullet points!).
Do they have any comments or questions?
If so, write them down.
Non-Contact ForcesNon-Contact ForcesLearning Objectives
To be able to:
Give examples of forces which don’t need objects to be in contact
Explain the difference between mass and weight
How is gravity like magnetism … and how is it different to
friction?
Starter thinking skillsStarter thinking skillsLook at the table. What does it tell you?
Distance of magnet (cm)
Force on iron nail (N)
2 2.0 4 1.0 6 0.6 8 0.4
10 0.3
Tables present data, helping us to answer questions and see patterns in results.
What questions could you ask about this table that others in your class could answer?
Distance of magnet (cm)
Force on iron nail (N)
2 2.0 4 1.0 6 0.6 8 0.4
10 0.3
QuestionsQuestions1. The lift in a tall building hangs from a strong
cable. The movement of the lift is affected by only two forces. These forces are the tension in the cable and the weight of the lift.
(a) The lift is not moving. How do the sizes of the
two forces compare?
(b) When the lift is moving upwards and its speed is increasing, how do the sizes of the two forces compare?
(c) When the lift is moving upwards at a constant speed, how do the sizes of the two forces compare?
(d) Near the top of the building the lift is moving upwards, but slowing down.How do the sizes of the two forces now compare?
weight
cabletension
lift
Assessing what we have Assessing what we have learnedlearned
Learning Objectives
To be able to:
Identify what we have learned so far in this topic
Did you have any surprises in the
work you did today?
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