1. AQA GCSE Physics 3-1b Turning Forces Circular, Satellite & Planetary Motion
GCSE Physics pages 222 to 233
April 10th 2010

2. AQA GCSE Specification
CIRCULAR MOTION
13.2 What keeps bodies moving in a circle?
Using skills, knowledge and understanding of how science works:
• to identify which force(s) provide(s) the centripetal force in a given situation
• to interpret data on bodies moving in circular paths.
Skills, knowledge and understanding of how science works set in the context of:
• When a body moves in a circle it continuously accelerates towards the centre of the circle. This acceleration changes the direction of motion of the body, not its speed.
• The resultant force causing this acceleration is called the centripetal force.
• The direction of the centripetal force is always towards the centre of the circle.
• The centripetal force needed to make a body perform circular motion increases as:
– the mass of the body increases;
– the speed of the body increases;
– the radius of the circle decreases.
SATELLITE AND PLANETARY MOTION
13.3 What provides the centripetal force for
planets and satellites?
Using skills, knowledge and understanding of how science works:
• to interpret data on planets and satellites moving in orbits that approximate to circular paths.
Skills, knowledge and understanding of how science works set in the context of:
• The Earth, Sun, Moon and all other bodies attract each other with a force called gravity.
• The bigger the masses of the bodies the bigger the force of gravity between them.
• As the distance between two bodies increases the force of gravity between them decreases.
• The orbits of the planets are slightly squashed circles (ellipses) with the Sun quite close to the centre.
• Gravitational force provides the centripetal force that allows planets and satellites to maintain their circular orbits.
• The further away an orbiting body is the longer it takes to make a complete orbit.
• To stay in orbit at a particular distance, smaller bodies, including planets and satellites, must move at a particular speed around larger bodies.
• Communications satellites are usually put into a geostationary orbit above the equator.
• Monitoring satellites are usually put into a low polar orbit.

3. Centripetal Force Recap of Forces The meaning of centripetal force
The three factors on which centripetal force depends 1 2 3
Why an object moving in a circle has an inward acceleration

4. Complete sheet on Terminal Velocity
Task
Complete sheet on Terminal Velocity

5. Centripetal Force
CENTRIPETAL FORCE is the general name given to a centrally directed force that causes circular motion.
Tension provides the CENTRIPETAL FORCE required by the hammer thrower.

6. Other examples of centripetal force
Situation
Centripetal force
Earth orbiting the Sun
GRAVITY of the Sun
Car going around a bend.
FRICTION on the car’s tyres
Airplane banking (turning)
PUSH of air on the airplane’s wings
Electron orbiting a nucleus
ELECTROSTATIC attraction due to opposite charges

7. Factors affecting centripetal force
INCREASES if:
- the object is moved FASTER
- the object’s mass is INCREASED.
- the radius of the circle is DECREASED.

8. Centripetal Force
Why does an object moving in a circle have an inward acceleration ? When an object moves in a circle, there is unbalanced force on it that acts towards the center of the circle. Newton 2 what happens if an object has an unbalanced force on it?

9. Acceleration- How?
Acceleration is the change in velocity / time Remember velocity is a vector – speed and direction So we have ……..

10. What happens if the string breaks?
What direction does the ball move? Remember Newton 1 String breaking quiz Draw on the diagram provided

11. Tasks
Do questions 1- 4 on page 49 Question 12 on page 51 Fill in missing words

12. Choose appropriate words to fill in the gaps below:
An object will only move along a __________ path if it is constantly acted on by a centripetal _________. The force is always directed __________ the centre of the circular path.
Centripetal force ___________ if the object moves in a smaller radius path or at a __________ speed.
An example of a _________ force is the Moon orbiting the Earth due to the Earth’s _____________ pull on the Moon.
circular
force
towards
increases
greater
centripetal
gravitational
WORD SELECTION:
gravitational
force
greater
circular
towards
centripetal
increases

13. Centripetal Force Recap of Forces The meaning of centripetal force
The three factors on which centripetal force depends 1 2 3
Why an object moving in a circle has an inward acceleration

14. Circular Motion Simulations
Ladybug Revolution - PhET - Join the ladybug in an exploration of rotational motion. Rotate the merry-go-round to change its angle, or choose a constant angular velocity or angular acceleration. Explore how circular motion relates to the bug's x,y position, velocity, and acceleration using vectors or graphs.
Motion in 2D - PhET - Learn about velocity and acceleration vectors. Move the ball with the mouse or let the simulation move the ball in four types of motion (2 types of linear, simple harmonic, circle). See the velocity and acceleration vectors change as the ball moves.
Motion produced by a force - linear & circular cases - netfirms
Uniform circular motion - Fendt
Carousel - centripetal force - Fendt
Relation between speed and centripetal force - NTNU
Vertical circle & force vectors - NTNU
Circular Motion & Centripetal Force - NTNU
Inertia of a lead brick & Circular motion of a water glass - 'Whys Guy' Video Clip (3 mins) (2nd of 2 clips)

15. Gravitational attraction
Gravity is an attractive force
Gravity depends on mass and the distance between objects.

16. Gravitational field strength
Gravitational field strength is equal to the force exerted on an object of mass 1kg.
On the Earth’s surface the gravitational field strength is about 10 N/kg (okay 9.81 N/kg)
Moon’s surface = 1.6 N/kg
Mars’ surface = 3.7 N/kg
Weight is the force of gravity on an object.

17. Gravitational attraction
Gravity is a force exerted by all objects on each other.
Gravitational force:
- is always attractive
- increases if the mass of the objects is increased
decreases if the distance between the objects is increased – it is inversely proportional
P.S These are Sir Isaac Newton’s rules on Gravity

18. Complete Answers Earth 10 80 Moon 1.6 Mars 3.7 740 Jupiter 60 1500
Surface
Field Strength (N/kg)
Object mass (kg)
Object weight (N)
Earth 10 80
Moon
1.6
Mars
3.7
740
Jupiter 60
1500
Pluto
0.07
800
128
200 25
5.6

19. Choose appropriate words to fill in the gaps below:
Gravity is a force exerted by all ________ on each other because of their ________.
Gravitational force __________ if the distance between the objects is increased but __________ if their masses are increased.
_________ is the force of gravity on an object. On the Earth’s surface an object of mass 1kg has a weight of 10 __________.
The Moon’s gravity is about one sixth the strength of the Earth’s because its _________ is much lower.
objects
masses
decreases
increases
weight
newtons
mass
WORD SELECTION:
increases
newtons
objects
decreases
masses
mass
weight

20. Gravitational attraction Notes questions from pages 224 & 225
State Newton’s rules on gravity.
Copy and answer questions (a) and (b) on page 224.
Describe how the force of gravity on a space vehicle changes as it travels from the Earth to the Moon.
Copy and answer question (c) on page 224.
Define what is meant by ‘gravitational field strength’. Show that a mass of 200 kg weighs approximately 32 N on the Moon.
Copy and answer question (d) on page 225.
Copy the ‘Key points’ table on page 225.
Answer the summary questions on page 225.

21. Gravitational attraction ANSWERS
In text questions:
The force of gravity on it due to the Sun.
Their mass is too small.
The force of gravity on the Moon is less, so less energy would be needed to escape from the Moon.
The force of gravity due to the Earth.
Summary questions:
(a) Increases
(b) Stays the same
(c) Decreases.
2. (a) The force of gravity is less on the Moon so it is easier for the astronaut to move up and down.
(b) The force of gravity is less on the Moon so the ball can go higher for the same change of gravitational potential energy.

22. Gravity Simulations Free-fall Lab - Explore Science
Galileo Time of Fall Demonstration - 'Whys Guy' Video Clip (3 mins) - Time of fall independent of mass - Leads slug and feather with and without air resistance. (1st of 2 clips)
Distance Proportional to Time of Fall Squared Demonstration - 'Whys Guy' Video Clip (3:30 mins) - Falling distance proportional to the time of fall squared. (2nd of 2 clips some microphone problems)
Lunar Lander - PhET - Can you avoid the boulder field and land safely, just before your fuel runs out, as Neil Armstrong did in 1969? Our version of this classic video game accurately simulates the real motion of the lunar lander with the correct mass, thrust, fuel consumption rate, and lunar gravity. The real lunar lander is very hard to control.
Moonlander Use your thrusters to overcome the effects of gravity and bring the moonlander safely down to earth.
BBC KS3 Bitesize Revision:
Mass and gravity
Weight

23. Planetary Orbits Gravity cause the planets to orbit the sun
The time it takes a planet to orbit depend on its distance from the sun

24. Planetary orbits
The orbits of the planets are slightly squashed circles (ellipses) with the Sun quite close to the centre.
The Sun lies at a ‘focus’ of the ellipse

27. Planetary orbits Notes questions from pages 226 & 227
Copy the table on page 227.
(a) What force is responsible for planetary motion? (b) Why is this force an example of centripetal force?
Explain how orbital speed affects the shape of a planet’s orbit.
State how (a) the speed and (b) the time taken to complete one orbit depends on a planet’s distance from the Sun.
Copy and answer questions (a) and (b) on pages 226 and 227.
Copy the ‘Key points’ table on page 227.
Answer the summary questions on page 227.

28. Planetary orbits ANSWERS
In text questions:
There would probably be a bigger variation of temperature each year. The tides would be more variable.
Its orbit is about 5 times bigger and it takes about 12 times longer, so it must travel slower than the Earth.
Summary questions:
(a) Satellite, Earth.
(b) Earth
(c) Satellite, Earth.
(d) Planet, Sun.
2. (a) (i) Jupiter (ii) Venus
(b) 49 km/s

29. Planetary Motion Simulations
My Solar System - PhET- Build your own system of heavenly bodies and watch the gravitational ballet. With this orbit simulator, you can set initial positions, velocities, and masses of 2, 3, or 4 bodies, and then see them orbit each other.
Multiple planets - 7stones
Planet orbit info - Fendt
Orrery of Inner Solar System - CUUG
The Solar System - Powerpoint presentation by KT
Solar system quizes - How well do you know the solar system? This resource contains whiteboard activities to order and name the planets corrrectly as well as a palnet database - by eChalk
Hidden Pairs Game on Planet Facts - by KT - Microsoft WORD
Fifty-Fifty Game on Planets with Atmospheres - by KT - Microsoft WORD
Fifty-Fifty Game on Planets that are smaller than the Earth - by KT - Microsoft WORD
Sequential Puzzle on Planet Order - by KT  - Microsoft WORD
Sequential Puzzle on Planet Size - by KT  - Microsoft WORD
Projectile & Satellite Orbits - NTNU
Kepler Motion - NTNU
Kepler's 2nd Law - Fendt
Two & Three Body Orbits - 7stones
Orbits - Gravitation program
BBC KS3 Bitesize Revision:
Gravitational Forces - includes planet naming applet

30. Satellites
A satellite is a lower mass body that orbits around a higher mass body.
- The Moon is a natural satellite of the Earth.
- The Hubble Space Telescope is an artificial (man-made) satellite of the Earth.
- The Earth is a satellite of the Sun.

31. Satellites Period of an orbit = time for one orbit of the earth
Geostationary satellites period of orbit is 24 hours, this means it stays in the same position in the sky
Polar satellites – orbiting every two or three hours and can scan the whole Earth every day

34. Geostationary Satellites
Geostationary satellites must have orbits that:
- take 24 hours to complete
- circle in the same direction as the Earth’s spin
- are above the equator
- orbit at a height of about km
Uses of communication satellites include satellite TV and some weather satellites.

36. Question
What are the advantages / disadvantages of using a polar orbiting rather than a geostationary satellite for monitoring?
ADVANTAGES
- it is nearer to the Earth allowing more detail to be seen and
- it is easier to place into orbit
- it eventually passes over all of the Earth’s surface
DISADVANTAGE
- unlike a geostationary satellite it is not always above the same point on the Earth’s surface so continuous monitoring is not possible

38. Choose appropriate words to fill in the gaps below:
A satellite is a ________ mass object orbiting around a ________ mass body.
The larger the orbit of a satellite the more ________ it moves and the ________ it takes to complete one orbit.
Geostationary satellites are used for _____________ and have an orbital period of _____ hours.
_____________ satellites normally use polar orbits.
lower
higher
slowly
longer
communications 24
monitoring
WORD SELECTION:
monitoring
higher
communications
longer
lower 24
slowly

39. Satellites Notes questions from pages 228 & 229
With the aid of a diagram explain how a satellite can remain in orbit about the Earth.
How does (a) the speed and (b) the period of a satellite vary with its height above the Earth?
Copy and answer questions (a) and (b) on page 228.
(a) What is meant by a ‘geostationary orbit’? (b) Why must satellite TV use geostationary satellites?
What are ‘monitoring satellites’? What type of orbit is used for this type of satellite?
Copy and answer question (c) on page 229.
Copy the ‘Key points’ table on page 229.
Answer the summary questions on page 229.

40. Satellites ANSWERS In text questions:
It can give the location and the height above sea level. 12
They would be slowed by drag from the atmosphere and would fall back to Earth.
Summary questions:
(a) High, equator.
(b) Low, poles.
2. (a) (i) Below (ii) Above
(b) Less energy is needed because the orbit is nearer the ground than a geostationary orbit is.

41. Satellite Simulations
Electromagnetic Spectrum & Communications - BT
Inside a communication satellite - BT
Projectile & Satellite Orbits - NTNU
Newton's Cannon Demo - to show how orbits occur - by Michael Fowler
Kepler Motion - NTNU
Kepler's 2nd Law - Fendt
Space craft control - NTNU
How a satellite orbits - BT
Satellite orbits - BT
BBC KS3 Bitesize Revision:
Satellites & Space Probes

42. Turning issues Notes questions from pages 230 & 231
No questions.