Glossary

1.Air Resistance A force which slows objects moving through air

2.Compress To make smaller or squeeze together

3.Expand To make bigger or stretch

4.Force A push or a pull on an object

5.Gravity The pull force between objects such as the Earth and us

6.Magnet A metal object that can attract iron or steel

7.Mass The amount of material in a certain amount of space

8.Newton A unit of force

9.Newton meter An instrument that measures pull forces or weight

10.Water resistance(Up-thrust)

A force that slows objects moving through water

11.Weight The force exerted on a certain mass by gravity

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PushPull Twist

Small ForceBig Force

Big force acting to the LEFTSmall force acting to the RIGHT

Result moves to the LEFT

Forces

A force is either a push or a pull or a twistForces can make things:

1) Speed up 3. Change direction2) Slow down 4. Change shape

Forces are measured in Newtons (N)Forces are often measured using a spring balance called a force meter (or Newton meter)

Arrows show Direction and Size of a force

If two forces push or pull against each other and one is bigger than the other- the bigger one wins.

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Dog pulling on a lead

A ScrewdriverHand opening a draw

Boy kicking a ballHand turning a door knob

Forces

In each box, draw the picture described in the title. Underneath each picture, write what type of force it is: a push, a pull or a twist. On each picture, draw an arrow to show the direction of the force.

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Forces

Now draw 2 more pictures showing a push, two more showing a pull and two more showing a twist.

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Measuring Forces

Weight is the force we all know, it is what keeps us on the ground. Force is measured using a force meter (often called a Newton meter) Force is measured in units called Newtons (N)

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Measuring Forces

Working with a partner, use a force meter with a suitable scale to find the weight of your pencil case, a book, a shoe and anything else that is easily available in your classroom. Design a chart to record your results.

Object Weight

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Object

Weight in N

ewtons

Balanced forces

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Up-thrust is a force

Up-thrust is the Force Pushing Up on an object in Water (or Air)You’ve probably seen that things weigh less when they are held in water. This is because the water pushes up and cancels out some of the force of gravity pulling down.1) Up-thrust is much greater in water than in air.2) The size of the up-thrust in water has been pushed out of the way by the

object. A large object pushes away loads of water so the up-thrust is big.

Gravity equals up-thrust so the ball floats. The forces are balanced, so there’s no movement.The deflated beach ball sinks because now the up-thrust is smaller, and less than gravity. When the up-thrust is EQUAL to the force of GRAVITY, an object will FLOAT because the two forces are BALANCED.

Watch out! Don’t fall into the trap of thinking that because an object is big that it will necessarily float better. After all- which would you rather have on your foot- a bucket of concrete or a bucket of polystyrene?We say the concrete is denser- it’s a lot heavier for its size. Because it’s a lot heavier, the force of gravity pulling it down is a lot more. That’s why the concrete sinks and the polystyrene floats- even though the buckets are the same size.

Gravity won’t get you down- if you’ve got support….This is really important! Things don’t stay in place because gravity has got less but because there is force acting in the opposite direction. Don’t go writing anything like “it floats because gravity doesn’t go through water” either, because that’d be dead wrong.

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The Force of Friction and Air Resistance

Friction occurs when two surfaces touch each other

1) Rough surfaces slow things down a lotRoads are rough to help you slow down quickly.2) Smooth surfaces don’t slow you down as much3) Friction gives us grip4) Friction produces heat

Air Resistance Slows Down Moving Objects1) Air slows you down as you move through it- just like trying to wade through

deep water- only not nearly so bad.2) To travel faster through air, things need to be streamlined.3) To travel slower through air, you need a large surface area (like a

parachute).

Go on- Force yourself to get to grips with this section…Friction acts when things touch and air resistance slows you down when you move. Think about how easy or hard it is to slide on different surfaces. Don’t forget, even though friction tends to slow things down it can be pretty useful. If there wasn’t any friction everything would just slide out of your hands. Remember that the bigger the area you’ve got, the more air resistance you’ll feel.

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The Force of Gravity

You’ve learnt about two exciting forces with fancy names on the last page- now there’s another one for you to learn- gravity.Gravity pulls objects down towards the Centre of the Earth

1) Gravity pulls you down whether you are in the air, in the water or standing on the ground.

2) The size of the gravitational force is pretty much the same all over the Earth. You would have to be a very long way from the Earth before you no longer felt the effect of its gravitational pull.

Three Great Ways to Beat Gravity1) Exert a force in the opposite

direction.2) Support yourself on a strong

object- but make sure it is strong enough.

3) In water, if the up-thrust matches the pull of gravity you will stay afloat.

Gravity- Very down to earthRemember that gravity pulls us towards the centre of the Earth, so it keeps us stuck on the Earth’s surface. On the moon, you feel the moon’s gravity rather than the Earth’s. The moon is smaller than the Earth, so the force of gravity is less and you don’t get pulled down as much.

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1. Ali and Sarah weighed a brick suspended in air using a Newton meter. Then

they weighed the same brick in water,

with the same Newton meter. What

did they notice about the two

measurements? Why does this

happen?

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

_____________________________________________________________

2. What is the name of the force that keeps us on Earth?

_____________________________________________________________

3. “When you walk on the Moon, it’s like being on Earth but you are much

heavier,” said Karen. “No,” said Ali. “On the moon you are much lighter.”

Who is right and why?

_____________________________________________________________

_____________________________________________________________

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_____________________________________________________________

_____________________________________________________________

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1. What forces are acting on the parachute and the parachutist?__________________________________________________________________________________________________________________________

Draw arrows next to the picture to show the direction of the forces. Remember to label your arrows showing which force is which.

2. Joseph and Sam were investigating friction using a slippery bench to find out which shoe had the best grip. When the shoe began to slip, they marked the level on the bench. Here is a drawing of their experiment

a) Which shoe had the highest friction?_____________________________________________________________

b) Which shoe had the lowest friction?_____________________________________________________________

c) Which shoe would allow them to walk up the slippery bench safely? Why?_____________________________________________________________

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Balanced ForcesWhen forces are balanced- things don’t start to move1) The boat floats because the up-

thrust (upward force) is equal to gravity (downward force)

2) No one is going anywhere here because the force of the donkey pulling one way equals the force of the man pulling the other way.,

3) The balloon is suspended in the air when the up-thrust from the hot air equals the pull of gravity.It’s air resistance NOT up-thrust that stops a parachute falling too quickly.

4) The table is pulled down by gravity, but the floor balances this and pushes upwards (we say it provides an upthrust) so the table does not move.

5) The weight is suspended because the pull of the spring equals (is balanced by) the downward pull of gravity on the weight.

Balanced Forces- they’re still not moving me...The point to remember here is that just because something is still, it doesn’t mean there are no forces acting on it. When two forces are balanced, they cancel out, so the thing doesn’t move.

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Unbalanced ForcesWhen Forces are unbalanced, things get moving1) Gravity is greater than the up-thrust, so

the boat moves and unfortunately sinks.

2) The push from the elastic is greater than the air resistance or gravity so the missile shoots away.

3) The force of gravity is much greater than air resistance or his up-thrust.

Magnets exert a force on other magnets or magnetic materials1) A north and a south pole attract each other.2) Two north poles repel each other.3) Two south poles repel each other.

Remember- Forces make things speed up, slow down, start or stop things moving. Moving at a constant speed means balanced forces.

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Different forces acting on an object can be shown by arrowsLook at the pictures. Can you work out which forces are acting in each one?Draw arrows on each picture to show the direction of the forces.

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Answer the following Questions:Forces:

1. What 3 ways do forces work?..........................................................................................................................2. What are the four things that forces can cause objects to do?..........................................................................................................................3. What are the units of force?..........................................................................................................................4. What instrument would you use to measure force?..........................................................................................................................5. In a tug-of-war, if both teams are pulling with equal force, what will

happen?..........................................................................................................................

Friction:1. What is friction?..........................................................................................................................2. What sort of surface should have a slide so that you could go down it

really fast?..........................................................................................................................3. What is the name of force that gives us grip?..........................................................................................................................4. Why do we have good grip on our shoes?

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.

.........................................................................................................................5. What will be made when 2 surfaces rub together?.........................................................................................................................

.

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Air Resistance:1. What is air resistance?..................................................................................................................................................................................................................................................2. What shape should an object be in order to travel faster through the air?..........................................................................................................................3. Name something that needs to travel slowly through the air. How does it

manage this?...................................................................................................................................................................................................................................................4. What two forces are acting on a helium balloon floating in the air?..........................................................................................................................

Gravity:1. What is the name of the force that pulls objects down towards the

centre of the earth? Is there anywhere on earth where you don’t feel the effect of this force?

.........................................................................................................................

.2. How do birds overcome the force of gravity and stay up in the air?....................................................................................................................................................................................................................................................3. To stop a table in your classroom falling through the floor, what must

the floor do against the force of gravity pulling the table down?..........................................................................................................................

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.........................................................................................................................

.4. Why is it dangerous to jump off a tall building? Explain this in terms of

forces acting upon you...........................................................................................................................

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Up-thrust:1. What 2 forces are acting on an object floating in water?.........................................................................................................................2. What does the word up-thrust mean?.........................................................................................................................3. If you use some plasticine to make a large boat shape, it will float, but if

you use the same amount of plasticine to make a small round ball, it will sink. Why is this?

.........................................................................................................................

.........................................................................................................................

.........................................................................................................................4. In terms of the forces acting upon it, why does a boat float?.........................................................................................................................

Magnets:1. When do two magnets repel one another?.........................................................................................................................2. When do two magnets attract each other?.........................................................................................................................

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Match the following statements:A force changes in Newtons

A force has magnitude the shape, speed, direction of something

A force is drawn and direction

A force is measured as a force arrow

Decide whether the following statements are true or false. Correct the false ones:1. If a toy truck is not moving, the forces on it are balanced.

..............................................................................................................................

2. If an unbalanced force acts on the toy truck, it will start to complain.

..............................................................................................................................

3. If the toy truck is already moving and a force acts on it, its colour will

change.

..............................................................................................................................

4. If the toy truck is moving at a steady speed, friction equals the pushing

force.

..............................................................................................................................

Mention whether the following friction forces are useful or not:1. Air resistance of a parachute through air. (Useful/ Not useful)2. Air resistance of a car. (Useful/ Not useful)3. Friction between the soles of (Useful/ Not useful)

your trainers and the road.4. Friction between bicycle brakes and wheels. (Useful/ Not useful)5. Friction between moving parts of a machinery. (Useful/ Not useful)

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MagnetsWhat is a magnetic field?It is the field that surrounds magnetic materials and electric currents and are detected by the force they exert on other magnetic materials.

The ends of a bar magnet are called poles.One end of the pole is called the North seeking pole, and the other end is called the South seeking pole.Unlike poles attract each other (pull together)Like poles repel each other (push apart)

What do magnets attract?Magnetic metals: only !!!Iron, steel, Cobalt and Nickel

Non magnetic metals Ex.: Copper and Aluminum are not attracted by magnets.Non magnetic objects Ex.: Plastic and Wood are not attracted by magnets.

Magnets are used in lots of different things including speakers and credit cards.

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