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?