Forces and Gravity
Is gravity real or does the Earth just suck?
Supports National Curriculum Key Stage 2, Units 1E, 2E, 4E and 6E
Suitable for years 4,5 and 6.
The time for whole session is about 2 hours. This can be varied by taking shorter paths through the material. Choices may depend on the apparatus available or the particular needs of the class.
Outline of content
Aims to
-establish what the children already know, using demos and class experiments
-provide the children with a clear idea of what a force is
-relate movement to forces
-explain that gravity and weight are forces
-establish that forces can be measured and teach them to estimate the size of forces
-represent forces with arrows
-the forces are balanced on objects falling steadily
-teach that there is a force of gravity on the Moon but it is much smaller than on Earth
-teach that the planets orbit the Sun because of gravity
-excite the children’s interest
Points to note:
Please read the notes about safety and agree the assessment with the teacher before the session!
Cross References:
- The slides in the PowerPoint presentation are referenced in the table.
- As the presentation may be running throughout the session some simple slides provide a suitable background, alternatively switch to a black screen.
-Apparatus details are below the table and are linked to the relevant sections.
Vocabulary
The presentation uses expressions included in the KS1 2 strategies
Misconceptions to be corrected
-there is no gravity in space
-the Moon does not have a gravitational field
-heavy objects fall faster than light objects
-all objects are ‘weightless’ in space
I found that it was important to spend time on the very basic ideas of forces. They learned a lot from the games and these lead into discussions which I encouraged so that they could gain a clear understanding. Teachers, in each school, commented that their own understanding had been clarified.
Is gravity real or does the Earth just suck?
Activity / Discussion / Aims/factsShow Powerpoint Slide 1
1. Demonstration-to catch their interest.
Fix a large brightly coloured helium balloon with ‘blu tac’ conveniently near where you will be speaking. Walk in with large cardboard box (apparently very heavy) and hold it on the edge of convenient table, ensuring that the box can be seen to project a long way over the edge of the table.
View Apparatus List
Ask a child to attach the balloon to the end of the box away from the table. Leave go of the box which stays in place because there is a brick inside it, which is above the table.
Ask whether the box will fall if the balloon is removed. Once they have discussed this, ask a child to remove the balloon and show that the box is still balanced. Finally after discussion you might show them the brick.
Safety Note: Bricks are heavy and have sharp edges – ensure that the brick does not fall out of or through the bottom of the box onto toes. / Once the balloon is attached, ask whether or not the box will fall if you leave go of the box.
When you ask whether the box will fall if the balloon is removed, there could be a show of hands to vote. Ask them for reasons. They will explain in terms of what they already know.
Full understanding requires them to have some ideas about turning forces. There is no need to go into details but they have the opportunity to talk about sizes of forces and their directions. / To excite the children’s interest and to get them to contribute their ideas about forces. It is important to find out how much they already know on the topic.
2. Pushes and pulls
Have two toys, one that needs to be pulled (e.g. toy duck on wheels with string attached) and one that needs to be pushed. Invite two children to make the toys move.
To the child with the pushing toy give the word card with push on it, and to the other give the pull card.
Stand each child at each side of the room and tell the children that when they see a push they have to point to the ‘push’ card and when they see a pull they point to the ‘pull’ card. Then bring out more objects that need to be pushed or pulled and for each one ask a child to make it work. Large objects are best, including toys and springs.
View Apparatus List
Demonstrate the Airzooker- pushes air
Have some more complex ones with twists and turns too.
Safety Note: Toys and items brought in for children to handle to show forces should be safe – check that there are no sharp parts, that springs are secured and there are no places where fingers can be trapped. / Ideas about pushes and pulls are introduced at an early age.
Ask the other children to explain what each child did to make each toy move.
Ask the question what name do we give pushes and pulls? Hopefully get the answer – forces.
Alternatively the examples of forces can be handed round to groups of children and after a few minutes each group can report back. (Remember to collect all the articles by the end of the discussion so that the children are not distracted.) / To ensure that they have a clear understanding of what a force is.
3.
Show Powerpoint Slide 2 / Encourage them to say what changes happen when forces act. The show slide 2 / To relate movement to forces. Forces start something moving, change its speed or change its direction.
Forces will also change the shape of an object.
4. Show Powerpoint Slide 3
Big and little forces
Measuring forces
View Apparatus List
Use a forcemeter to push and pull and show sizes of forces.(Maybe relate to length of a spring) / Discuss the push of a feather resting on a hand. Then the push needed to bend the tree—
These measure forces by the change in shape they produce. / There are large forces and small forces
These can be measured using a forcemeter (newton meter)
5. Gravity
Drop a soft object / Ask what made it fall - it moved so there must have been a force on it—was it a push or a pull?
What do we call the force? Gravity /
Gravity is a force
6.Story about Sir Isaac Newton and a fruit dropping on his headShow Powerpoint Slides 4, 5 and 6
What fruit? —Satsuma, apple, melon
Vote
Show Powerpoint Slide 7 / Ask them which fruit is most likely to have dropped on Newton’s head. Ask for reasons using the opportunity to talk about different weights.
Ask whether the man in the picture (slide 6) could be Newton- wrong clothes- emphasize that Newton lived 300 years ago. (1643-1727) / Idea that people had seen apples drop for thousands of years but it took Newton to think and understand about gravity. Many of the most important scientific ideas have come from thinking about something that others take as usual or even as a mistake.
Weight is a force
7. Hazards and risks(Could be part of discussion or be omitted)
Hazard – stopping something moving can injure.
Risk – small for slow, light objects.
- high for fast, heavy ones. / Small toy car moving slowly- safe to stop it.
Toy car moving quickly could be dangerous
Full size car moving- VERY dangerous if a person is in the way it will not stop. / Stopping things moving can be dangerous
Road safety – cars
8. The unit of force is a newton – after Isaac Newton. / The unit of force is a newton- named after Isaac Newton.
9. Hand round some small objects with the weight of about 1 newton.
View Apparatus List
At end of this showShow Powerpoint Slide8 / Discuss examples of objects weighing about 1 newton.
Bring out the idea that 1 newton is approximately the weight of a small eating apple.
Talk about estimating the forces / Any thing with a mass just over 100 g weighs about 1 newton on earth.
This helps them to have a memory of the size of a newton.
10. Slide 9
Mystery BOX
View Apparatus List(see diagram 1)
First ask volunteers to pull a string and estimate the size of the force in newtons.
Put the results in a table. (Fill in the table on Slide10, if a white board is used. Otherwise take some sheets of paper with tables printed on for groups to fill in the values in case no board is available.)
Safety Note: Mystery box could cause children to hurt their fingers on the stringensure that the maximum weight is not large
Then ask more children to use a suitable forcemeter to check values. / Discuss their answers. / Reinforces a memory of the size of a newton.
Introduces the idea of estimating.
11. (Show Powerpoint Slide11 if helpful)
Safety Note: High range forcemeters may be unsafe for small children – avoid forces greater than 10 N.
12.Game (Show Powerpoint Slide 12)
Ask for volunteers and pass a ping-pong ball around using straws through which the children need to suck to overcome the effects of gravity; try with heavier objects.
Show Powerpoint Slides13 , 14
View Apparatus List
Safety Note: Straws present a hygiene hazard - do not reuse or allow them to be passed round. / They find this works best if the straw points straight downward because then it is in the direction of the force of gravity acting on the ball. Discuss the directions of the arrows on the slides.
The game with the ping pong balls helps them to understand that to pull against gravity they must have the straw vertical. / An upwards pull is needed against gravity.
Links in with the title of the session.
When the ball does not fall the upward force caused by sucking = the force of gravity on it.
13. Drawing forces
Show Powerpoint Slides 15,16,17
(Ignoring air resistance,) falling objects have only one force acting on them
Object on string or held by a straw has two equal forces, one up and one down. / Discuss how to show that the “sucking force” is equal in size to the force of gravity on the ball when the ball is held still. / Forces can be represented by arrows which show the direction and the size.
14. Newton’s brainwave- GRAVITY
Every object pulls every other object towards it—Gravity
For small objects, the force is very small.
The Earth is very large and has a lot of ‘stuff’ in it and therefore the pull is large enough to feel and so objects are pulled towards the Earth when free to fall. / Gravity is a force which acts between ANY two objects.
15. In Australia people are attracted to the Earth as we are – they do not fall off!
Show Powerpoint Slide 18 (could be omitted if does not arise in the discussion) / They may ask ‘Shouldn’t the people in Australia be upside down?’
16 Air resistance
Drop a phone book and a ping pong ball- both hit the ground at the same time—use other demos if available.(Show Powerpoint Slide19)
View Apparatus List / Slide 19 shows a steel ball gaining slightly on the ping ball. / Explain that in Slide 19 the light flashes regularly so the positions of the objects are shown at the same moment.
17. Dropping object on the Moon
Video Show Powerpoint Slide20
Video of two objects falling on the Moon – hammer and feather / Discuss how the feather would fall on Earth
Compare the effect of dropping a feather on the Moon and on the Earth / No atmosphere on Moon so no air resistance. If they are released at the same instant, both the heavy object and the very light object reach the ground at the same time.
18. Air Resistance
(The following could be omitted)
Talk about the time taken for falling objects to reach the floor. Then use a sheet of paper and the ping pong ball-
Experiments with parachutes to show there is air resistance—a force caused by the air that acts in the opposite direction to the downward movement.
The larger the load the sooner the parachute reaches the ground.
The larger the area the longer it takes for the parachute to reach the ground
Show arrows for forces- weight same size throughout
When getting faster (accelerating) the weight is larger than the air resistance force.
NB They do not need the word acceleration.
This could lead to a parachute investigation by the teacher at a later date.
An example of a simple paper parachute is in the extra list.
Safety Note:Parachute investigation (extra): Any activity which might cause objects to be thrown can present hazards. The risks are small if the paper parachutes are dropped carefully. Children must not be allowed to stand on chairs, desks or above stairwells without adequate supervision to drop the parachutes. / Tell them a story about Hippo, who jumped out of a plane. Ask them how they could save Hippo—a parachute.
Ask whether the parachute in slide 23 would save Hippo.
-No- the air would spill out.
Show slide 24, ask if Hippo is safe. – Still falling very quickly.
Show slide 25 and talk about the force of the air resistance being equal in size to force of gravity on Hippo- steady speed.
Slide 26 Ask what change could be made so that Hippo slows down- larger parachute / Air resistance acts to slow down moving objects.
Large surfaces cause larger air resistance than small surfaces.
18. Satellites
Show Powerpoint Slide27
Satellites have to move very quickly to orbit the Earth / Discuss what happens when they throw a ball- it drops to the Earth.
If an object is projected at VERY high speed then it goes further round the Earth.
An object must be moving at high speed to orbit the Earth.
Talk about satellites and the fact that the Moon is a satellite of the Earth. / The Moon orbits the Earth. The Moon is moving in a path around the Earth.
19. The Moon
Moon smaller than Earth (Show Powerpoint Slides28 & 29)
Get them to reason out that the force of gravity on the Moon is much smaller than the force of gravity on the Earth
Discuss consequences
When a person walks they are used to having to push away from the Earth so on the Moon they would push high off the surface with the strong muscles they have. (Show Powerpoint Slide 30)Therefore heavy boots are worn to keep them from bouncing high above the surface. (Show Powerpoint Slide 31) / The more material (stuff) in an object the larger the force of gravity between it and other objects.
They will think that there is no gravity on the Moon. Reinforce that there is a force of gravity between ANY two objects. / The Moon is many times smaller than the Moon so gravity on Moon is very much smaller than on the Earth.
20. Zero Gravity
When going down in a lift you feel an odd sensation. This is because the lift floor is moving downwards and is not pushing up on your feet as hard as usual.
When in free fall there is a sensation that there is no gravity – Show Powerpoint Slide 32 / Use this to invite discussion about space travel and other applications.
(Powerpoint Slide 33 could be used to show that a falling object is apparently weightless.) / Understanding gravity has made space travel possible.
21. Ask them what it would be like if there was no gravity.
(Show Powerpoint Slides34, 35) / Encourage them to keep asking questions. / Scientists find answers to questions. Being an scientist is exciting.
To be inserted where it fits – depending on the group
"Every object pulls every other object toward it.
"The more matter (stuff) an object contains the harder it draws.
"The nearer an object is to another the harder it draws.
"The harder an object draws other objects, the heavier it is said to be.
"The earth is millions of times heavier than any object near to or upon its surface; so it draws every such object toward it.”
Apparatus List
List 1 -Activity 1
Demonstration 1
Large Cardboard box
Helium Balloon
Brick
List 2 (Activity 2)
List of suggestions of objects for them to try in order to experience forces:
Pushes and pulls
large springs- those from a chest-expander or similar are good,
a toy with a string to pull it,
toy car
Plasticine or similar.
Some examples of turning forces could be included: eg hand food whisk.
Airzooker- source Hawkin’s bazaar
List 3 (Activity 4)
Forcemeters (remember to order these from the school before your visit)
List 4 (Activity 9)