MODULE mod7A mod7B mod7C mod7D mod7E mod7F mod7G mod7H mod7I mod7J mod7K mod7L mod8A mod8B mod8C mod8D mod8E mod8F mod8G mod8H mod8I mod8J mod8K mod8L mod9A mod9B mod9C mod9D mod9E mod9F mod9G mod9H mod9I mod9J mod9K mod9L 7ka1
7Ka/1 Forces in action
Name _____________________________ Class ____________
Fill in the gaps on this sheet. The words you need are given in the brackets.
1
Apparatus
- 2 magnets
The magnets are _____________________ (attracting/repelling) each other.
The force is strongest when the magnets are _____________________ (close together/far apart).
The name of this force is _____________________ (friction/gravity/magnetism).
What will happen if you turn one of the magnets round? __________________________________
________________________________________________________________________________
2
- ice cube
- wooden block
The force of _____________________ (friction/gravity/magnetism) tries to stop the blocks moving
across the desk.
It is _____________________ (easier/harder) to push the block of ice, because the ice is
_____________________ (smoother/rougher).
3
- natural string
- plastic string
It is _____________________ (harder/easier) to tie a knot in the plastic string. The plastic string
has a _____________________ (rough/smooth) surface so there is less _____________________
(friction/gravity/magnetism).
4
- spring
The force from the spring gets _____________________ (bigger/smaller) if it is stretched further.
The spring is _____________________ (pulling/pushing).
5
- force meter
- object
Weigh the object.
How much does your object weigh? _____________________
The force of ____________________ (friction/gravity/magnetism) is pulling the object downwards.
6
- Two sheets of paper
The paper takes _____________________ (less time/more time) to fall if it is crumpled up. The air
resistance is _____________________ (more/less) when the paper is crumpled up.
[ observing ]
7Ka/2 Contact and non-contact forces
1 Cut out the five pictures and five labels at the bottom of the page.
2 Stick the forces in the correct boxes.
3 Stick the correct label below each picture.
Non contact forces
Contact forces
---------------------------------------------------------------------------------------------------------
Magnetism
Static electricity
Friction
Gravity
Upthrust
[ knowledge ]
7Ka/3 Forces are everywhere
1 Which forces are pushes and which ones are pulls? Write the correct words in the spaces.
_________________
2 Look at the pictures below. Write the names of the forces next to the arrows.
A
_____________
B
C
D
E
F
3 Which pictures show non-contact forces? ___________________
4 Complete these sentences.
a A ___________________ is needed to start an object moving.
b A force can change the ___________________ , ___________________ and
___________________ of an object.
c Nothing starts to move without a ___________________ being involved.
d Three forces which can act from a distance are ___________________ ,
___________________ and ___________________ ___________________ forces.
7Ka/4 Find the forces
Write the answers to the clues in the spaces.
Clues Answers
a A force which pulls you down. ____________________
b This force helps to hold things to fridge doors. ____________________
c This type of force needs to touch something to affect it. ____________________
d This force rubs things away. ____________________
e This force helps a ship float. ____________________
f A form of electricity which can attract things. ____________________
Now try to find the words in the wordsearch. Mark all the contact forces in red and the non-contact forces in blue.
(Use pen and pencil if you do not have any coloured pencils.)
W
R
I
T
O
N
S
P
Y
Q
L
H
U
M
J
V
G
K
Z
[ knowledge, literacy ]
7Ka/5 Which way is the force acting?
Mark the diagrams with arrows to show the forces. Most of the pictures have more than one force. Write in the name of each force.
Think about whether the forces are balanced or not. When you draw arrows to show balanced forces, both arrows should be the same size.
If the forces are unbalanced, the biggest force should have the biggest arrow.
The first one has been done for you.
7Ka/6 Bathroom scales
How do bathroom scales work? There is no space inside for a long spring, like the ones in force meters. And how does the dial go round? Scales measure your weight, which is the force of gravity pulling on you.
This diagram shows a simplified version of what happens inside a set of bathroom scales. Real scales are a bit more complicated than this. They need more bits and pieces to make sure that everything fits into a fairly small, flat case.
When you stand on the scales you are pushing down on a lever that is attached to the spring. The lever and spring are arranged so that you do not make the lever move very far - this is so everything can fit inside a small case. The end of the lever moves a rack, which is a long piece of metal with teeth along one side. The rack is touching a pinion, a wheel with teeth on it. The pinion is attached to a round dial which has the weights marked on it. When the rack moves down, it turns the pinion, which turns the dial. When you stand on a set of scales you can see the dial moving. The number on the dial that ends up under the pointer shows your weight. Most bathroom scales turn your weight into a reading of your mass in kilograms.
1 a What is the name of the force that is pulling you down when you stand on a set of bathroom scales?
b Is this a contact force or a non-contact force?
2 What is the weight of the person standing on these scales?
3 If a heavier person stood on the scales:
a would the spring be stretched more or less than it is now
b would the rack move up or down?
4 Do you think the spring in the bathroom scales is harder to stretch than the ones in the force meters you use in school? Explain your answer.
5 These scales will weigh someone as heavy as 1300 N. How could the scales be changed so that they could weigh a heavier person?
6 You want to weigh your baby sister, but she is too young to be able to stand on the bathroom scales. How could you weigh her using the scales?
7Kb/1 Floating, sinking and density
Is there a connection between the density of an object and whether it floats or sinks?
Density measures how much mass there is in 1 cm3 of something. You have to work it out from a mass and a volume.
- Different materials
- Bowl
- Ruler
- Water
- Calculator
- Balance
Method
1 Make a table for your results, like this:
2 Choose a material, and write its name in your table.
3 Use a balance to find its mass, and write it in your table.
4 Measure the length, height and width of your material, like this:
Write the measurements in your table.
5 Multiply the three measurements to find the volume of your material.
6 Divide the mass by the volume you have just worked out. This is the density. Write it in the correct column.
7 Now see if your material floats or sinks. Write F or S in the last column.
8 Repeat steps 2 to 7 for other materials.
9 Write two or three sentences to describe what you did.
Considering your results/conclusions
1 Look carefully at your results. Do materials with high densities float or sink?
2 Copy and complete these sentences. Choose from the words in the brackets.
Density is a way of saying how much (mass/volume) there is in 1 cm3 of a material. A material with a high density feels (lighter/heavier) than a material with a low density.
Materials with a high density (float/sink) when you put them in water.
Materials with a (high/low) density float.
The density of water is 1 g/cm3. If a material has a density (less/greater) than the density of water, it will float.
[ observing, numeracy, considering ]
7Kb/2 Upthrust in different liquids
Does the amount of upthrust depend on the liquid?
You are going to find out if the amount of upthrust depends on the liquid. Even objects that sink have upthrust acting on them, but the upthrust is not big enough to make them float.
You can measure upthrust by finding out how much the weight of an object changes when you put it in water.
- Force meter
- Different liquids
- String
- Beaker
- Object
1 Write a method for your investigation. Remember to say how you will make sure that your investigation is fair.
Recording your results
2 Make a results table like this:
3 Carry out the experiment and fill in your table. You calculate the number in the fourth column using this formula:
Upthrust = weight in air - weight in liquid
4 You can find out more about your liquids using a balance. Measure out equal volumes of each liquid and find their mass. Work out the density and write your results in the last column of your table.
5 Does the upthrust depend on the kind of liquid?
6 What is the connection between the density of the liquid and the amount of upthrust it provides?
[ planning, observing, considering ]
7Kb/3 Floating questions 1
1 Josh was in the sea at high tide when he came across a large stone under the water. He tried to lift the stone and was surprised to find that he could move it easily. He returned at low tide and found the stone out of the water. This time he could hardly move it.
Use the words in the box to complete these sentences. Some words can be used more than once.
gravity upthrust water weight
a The stone felt lighter when it was under ________________ . This is because
________________ was helping to push it up.
b The stone does not float because its ________________ is greater than the
________________ .
c The two forces which affect the stone are ________________ and ________________ .
2 This is Danny floating in the water. Label the two forces.
________________
3 Your weight is 600 N and you have just finished building a raft which weighs 1000 N.
a What is the total weight of you and the raft? ________________
b What is the smallest upthrust force needed so that it will just float with you on it.
______________________________________________________________________
7Kb/4 Floating questions 2
1 What force holds a hot air balloon in the air?
2 Your weight is 600 N and you have just finished building a raft which weighs 1000 N.
a What is the total weight of you and the raft?
3 The pictures below show objects that have just been placed below the surface of the water. The arrows show the direction and size of the forces affecting each object.
a Which object will sink?
b Which object will just float in the water?
c Which object will float well and be able to carry a small load?
4 The table shows the masses and volumes of pieces of different materials.
Copy the table, and complete the last column.
Remember the formula for calculating density is:
Density =
Material
Mass (g)
Volume (cm3)
Density
Copper
1800
200
Wood
900
1500
Lead
567
50
Iron
790
100
Water
1000
Polythene
690
750
Glass
197
80
Plasticine
26
20
Bone china
42
15
Brick
3200
2000
5 Make a list of all the materials in the table that will float.
[ knowledge, numeracy ]
7Kb/5 The Plimsoll line
This story started about two hundred years ago in the early days of the British merchant navy. Greedy ship owners would often overload the ships with goods they wanted to sell in far-away countries.
Because they were so overloaded, many ships would sink if they met a storm at sea. The sailors' families had to wait for months before they knew if the crew had survived the trip. Many never came back - they were 'missing, presumed lost'.
In 1870, a member of Parliament called Samuel Plimsoll decided that too many ships were being lost at sea due to overloading. He passed a law forcing ship owners to have a special line painted on the side of each ship. Loading of the ship had to stop as soon as the water level reached this line. If the water level went above the line, the ship owners would be fined or imprisoned.
The 'Plimsoll line' is still in use today and can be seen painted on the side of all cargo ships. Ships also have load lines for different parts of the world. These are very important for ships which travel from the cold seas of Britain to the warmer tropical seas. Warm sea water produces slightly less upthrust than cold sea water, so ships float lower down in warm water. Fresh water also produces less upthrust than sea water.
1 Why did ship owners want to overload their ships?
2 Why was this dangerous?
3 What did Samuel Plimsoll force ship owners to do?
4 Why was it dangerous for a fully loaded ship to travel from the sea into a fresh water river?
5 There are two reasons why tropical fresh water produces less upthrust than water in winter in the North Atlantic. What are they?
6 A fresh egg is floating in a cup of water. You add lots of salt to the water in the cup. How does this affect the way the egg floats?
[ literacy, knowledge ]
7Kb/6 Archimedes
Archimedes lived in Syracuse, Italy, and was a great inventor and philosopher. One of the scientific facts that he discovered is called Archimedes' Principle. The upthrust on something in a fluid is equal to the weight of fluid displaced.
1 a What is the weight of the stone?
b What is the upthrust on the stone when it is in the water?
c What is the weight of the water in the small beaker?
d Why doesn't the stone float?
2 If you compared the weight of the stone in air with its weight in water, the difference would be the weight of the water displaced by the stone. This difference is the upthrust.
a What is the weight of the wooden block?
b What is the upthrust on the block?
d Why does the wooden block float?
3 All the beakers have water in them.
a Which object is the heaviest? How do you know?
b Write the three objects in order of their weight, starting with the heaviest. Explain how you worked out your answer.
4 a What would happen if you put a 1 N weight on top of block Z?
b What would the extra water in the small beaker weigh?
5 Some of the things Archimedes invented are still in use today. Find out what an 'Archimedes screw' is and what it is used for.
[ knowledge, numeracy, research ]