Key Theory Summary: Gravity, Weight, and Mass

1. Gravity

 Gravity is the force that pulls objects towards each other.

 The Earth pulls everything towards its centre because it has a large mass.
 The force of gravity is stronger with:
o Greater mass
o Shorter distance between objects

2. Weight

 Weight is the force of gravity acting on an object.

 It is measured in newtons (N).
 The equation for weight is:

Weight (N)=Mass (kg)×10 (N/kg on Earth)\text{Weight (N)} = \text{Mass (kg)} \

times 10 \, (\text{N/kg on Earth})Weight (N)=Mass (kg)×10(N/kg on Earth)

 Weight can change depending on location (e.g., on Earth vs. on the Moon).

3. Mass

 Mass is the amount of matter in an object.

 It is measured in kilograms (kg).
 Mass does not change with location.

4. Contact Force

 The force from a surface that pushes back against an object resting on it.
 Always equal and opposite to the weight of the object (if it's not moving).

A. Multiple Choice – Choose the correct answer

1. What causes the force of gravity?

A. Friction
B. Mass
 C. Light
D. Energy
2. What is the unit of weight?
A. Kilogram
B. Gram
C. Newton
D. Metre
3. What happens to gravity as you move further from Earth?
A. It increases
B. It disappears
C. It decreases
D. It stays the same
4. The equation to calculate weight is:
A. Weight = Mass + Volume
B. Weight = Mass × Gravity
C. Mass = Weight × 10
D. Volume = Mass × Length
5. The weight of a 2 kg object on Earth is:
A. 2 N
B. 20 N
C. 12 N
D. 200 N
6. What pulls objects towards the centre of the Earth?
A. Wind
B. Force of gravity
C. Inertia
D. Magnetic force
7. Which of the following changes when you go to the Moon?
A. Mass
B. Colour
C. Volume
D. Weight
8. What does the contact force do?
A. Pulls objects to Earth
B. Pushes up against weight
C. Increases gravity
D. Adds more mass
B. True / False

1. Gravity acts only on objects with very large mass.

2. The Moon has no gravity.
3. Weight is measured in kilograms.
4. Contact force pushes up with the same strength as weight (if balanced).
5. A 5 kg object has a weight of 50 N on Earth.
6. Mass can change if you go to space.
7. Gravity pulls objects towards the centre of Earth.
8. Newton is a unit of weight.

C. Fill in the Blank

1. Gravity always acts __________ the centre of the Earth.

2. The mass of an object is measured in __________.
3. Weight is measured in __________.
4. On Earth, the force of gravity is __________ N/kg.
5. The formula for weight is: weight = mass × __________.
6. Mass is the __________ of matter in an object.
7. When weight is balanced, the contact force is __________ to the weight.
8. The __________ pulls everything towards the Earth.

D. Short Answer

1. Describe how gravity affects a falling object.

2. What is the difference between weight and mass?
3. Why is weight different on the Moon compared to Earth?
4. Explain what a contact force is.
5. A book weighs 10 N. What is the size of the contact force from the desk?
6. A car has a mass of 1000 kg. What is its weight on Earth?
7. What direction does gravity pull objects on Earth?
8. If a rock weighs 8000 N, what must be the contact force from the ground?

Unit 3.2 – Formation of the Solar System

✅ Key Theory Summary

1. Origin of the Solar System

 Scientists believe the Solar System was formed from a cloud of dust and gas.
 Due to gravity, particles in the cloud were pulled together to form larger and
larger objects.
 As these objects grew, their mass increased, so their gravitational pull became
stronger, attracting even more dust and gas.
 Some objects eventually became stars (like the Sun), while others became
planets.

2. Solar System Structure

 All planets orbit the Sun in the same direction and lie in the same plane (a flat
surface).
 Most planets and moons spin in the same direction as their orbit.
 Venus spins in the opposite direction, which contradicts the model of how the
Solar System formed.

3. Nebula

 A nebula is a cloud of gas and dust in space.

 Stars (and Solar Systems) are born in nebulae.

4. Using Models in Science

 A scientific model is used to represent something that cannot be observed

directly.
 Models help scientists make predictions and explain or test a hypothesis (an idea
that can be tested).
 Example: Neptune was discovered after scientists noticed something strange
about Uranus’s orbit and predicted the presence of another planet.

🧠 Practice Exercises
🔹 A. Multiple Choice (8 Questions)

1. What did the Solar System form from?

A. Water and light
B. Cloud of dust and gas
C. Ice and metal
D. Fire and air
2. What pulls dust and gas together in space?
A. Air
B. Electricity
C. Gravity
D. Wind
3. What is a nebula?
A. A small planet
B. A cloud of gas and dust
C. A type of telescope
D. A moon
4. Which planet spins in the opposite direction to most others?
A. Mars
B. Venus
C. Earth
D. Jupiter
5. What shape is the orbit of planets in the Solar System?
A. Triangular
B. Square
C. Circular
D. Straight line
6. What does it mean that the Solar System is in the “same plane”?
A. All planets are the same size
B. All planets are flat
C. All orbits lie on the same flat surface
D. All planets move in straight lines
7. What helps scientists study things they cannot directly observe?
A. Telescopes only
B. Hypothesis
C. Models
D. The Sun
 8. Why do scientists use models?
A. To change facts
B. To guess randomly
C. To represent and explain observations
D. To avoid experiments

🔸 B. True / False (8 Questions)

1. Stars and planets formed from clouds of dust and gas.

2. Models are always 100% accurate.
3. A nebula is a star.
4. All planets in the Solar System spin in the same direction.
5. Gravity helps clump particles together in space.
6. The Solar System formed quickly, in a few years.
7. Models help explain how the Solar System was formed.
8. The direction in which most planets spin supports the model.

🔹 C. Fill in the Blank (8 Questions)

1. The Solar System formed from a __________ of dust and gas.

2. A __________ is a cloud in space where stars are born.
3. __________ is the force that pulls particles together.
4. Most planets spin on their __________.
5. A __________ helps explain or predict scientific ideas.
6. All planets orbit the Sun in the same __________.
7. Venus spins in the __________ direction compared to most planets.
8. Scientists look for __________ to support their hypotheses.

🔸 D. Short Answer (8 Questions)

1. What do scientists believe caused the formation of the Solar System?

2. What is the role of gravity in star and planet formation?
3. Describe what a nebula is and its role in the universe.
4. Why is Venus spinning in the opposite direction considered unusual?
5. What is a model in science?
 6. Why do scientists use models when studying space?
7. What is meant by planets orbiting in the “same plane”?
8. Give one fact that supports the model of the Solar System's formation and one that
contradicts it.

Key Theory Summary – 3.3: Movement in Space

1. What keeps planets in orbit?

 Gravity from the Sun pulls planets toward it.

 Planets move in a nearly circular path around the Sun.
 If there were no gravity, planets would move off in a straight line.

2. Vacuum

 Space is a vacuum, meaning it has no air particles.

 Because of this, objects in space do not slow down due to air resistance.

3. Speed of orbit

 Planets closer to the Sun move faster (e.g. Mercury).

 Planets farther from the Sun move slower (e.g. Neptune).
 This is because gravity is stronger when you're closer to the Sun.

4. Discovering planets

 Scientists use observations, predictions, and calculations to study planets.

 Neptune was discovered because Uranus’s orbit didn’t match predictions — this
hinted at another planet pulling on it.

Practice Exercises – Unit 3.3

A. Multiple Choice (8 questions)

1. What keeps planets in orbit around the Sun?

A. Magnetism
B. Gravity
 C. Electricity
D. Light
2. What is a vacuum?
A. A fast planet
B. A cloud in space
C. A place with no air
D. A black hole
3. Which planet moves the fastest around the Sun?
A. Mars
B. Jupiter
C. Mercury
D. Neptune
4. Which planet moves the slowest around the Sun?
A. Mercury
B. Venus
C. Earth
D. Neptune
5. Why do planets closer to the Sun move faster?
A. They are smaller
B. Sunlight pushes them
C. Gravity is stronger
D. They are hotter
6. What causes air resistance?
A. The Sun’s light
B. Objects rubbing against air particles
C. The Moon’s pull
D. Lack of oxygen
7. Why does Voyager 1 not reach planetary speeds?
A. It is too old
B. It travels in circles
C. It lacks enough force
D. It’s going in reverse
8. What did scientists use to discover Neptune?
A. A telescope only
B. Predictions and calculations
C. Moonlight
D. Observing Mars directly
B. True / False (8 questions)

1. Gravity pulls planets towards the Sun.

2. Planets move in a straight line around the Sun.
3. There is no air resistance in space.
4. Mercury moves slower than Neptune.
5. Scientists used predictions to find Neptune.
6. A vacuum is full of gases.
7. Planets move at the same speed around the Sun.
8. Uranus’ orbit helped scientists find Neptune.

C. Fill in the Blank (8 questions)

1. Gravity keeps the planets in __________ around the Sun.

2. A vacuum has no __________.
3. __________ is the planet with the fastest orbit.
4. __________ moves the slowest in orbit around the Sun.
5. Planets closer to the Sun move __________.
6. The force that slows moving objects on Earth is called __________.
7. Scientists used __________ to discover Neptune.
8. The orbit of __________ did not match predictions.

D. Short Answer (8 questions)

1. What would happen if the Sun’s gravity disappeared?

2. Why is space called a vacuum?
3. Describe how gravity affects the speed of orbit.
4. Why do objects move more easily in space than on Earth?
5. How did Uranus help scientists discover Neptune?
6. What is air resistance, and why is it not present in space?
7. What pattern do we observe in planet speed and distance from the Sun?
8. Why do scientists draw graphs to show orbit speed?
Unit 3.4 – Tides

✅ Key Theory Summary

1. What are tides?

 Tides are the regular rise and fall in the level of the sea.
 The difference between high and low tide is called the tidal range.
 Tides change every 6 hours – high tides and low tides happen about twice a day.

2. Causes of tides

 The Moon’s gravity pulls on the oceans, causing high tide on the side facing the
Moon.
 The Earth spins, so the same place moves from high tide to low tide in 6 hours.
 The Sun also causes tides, but its effect is weaker.
 When the Sun, Earth, and Moon are in a straight line, the tidal force is stronger –
this causes larger tidal ranges.

3. Effects of tides

 Tides affect harbours, fishing, and coastal safety.

 They are linked to earthquakes, volcanoes, and electricity generation (tidal
power).
 High tides can lead to flooding during storms.

4. Tidal terms

 High tide: Water level is highest.

 Low tide: Water level is lowest.
 Tidal force: The pull of gravity from the Moon and Sun.
 Tidal range: Difference in height between high and low tide.

🧠 Practice Exercises – Unit 3.4

🔹 A. Multiple Choice (8 Questions)

1. What causes tides on Earth?

A. Earthquakes
B. Gravity from the Moon and Sun
C. Wind from space
D. Ocean currents
2. What is the difference between high and low tide called?
A. Wave height
B. Tidal force
C. Tidal range
D. Water pull
3. How often do high and low tides happen each day?
A. Once
B. Twice
C. Three times
D. Four times
4. What causes the largest tidal ranges?
A. When the Moon is far away
B. When Earth, Moon, and Sun are in line
C. When there’s no gravity
D. When the Earth spins faster
5. What is true about low tide?
A. Water level is highest
B. The Moon is closest
C. Water level is lowest
D. It happens once a month
6. The Moon takes __________ to orbit the Earth.
A. 7 days
B. 27 days
C. 12 hours
D. 365 days
7. What is the pull of the Moon’s gravity on Earth’s water called?
A. Moonbeam
B. Orbital pull
C. Tidal force
D. Water stretch
 8. Why do some harbours only work at certain times of day?
A. The Sun moves too fast
B. Wind levels rise
C. Water depth changes with tides
D. Boats need low gravity

🔸 B. True / False (8 Questions)

1. The Moon has no effect on tides.

2. High tides happen when the Moon pulls water.
3. Tides always stay at the same level.
4. The Sun has no effect on tides.
5. Tidal range is the difference between high and low tide.
6. There are usually two high tides a day.
7. Tides are linked to earthquakes and volcanoes.
8. Tidal energy can be used to make electricity.

🔹 C. Fill in the Blank (8 Questions)

1. Tides are caused by the pull of __________ and __________.

2. The difference between high tide and low tide is called the __________.
3. Tidal forces are stronger when the __________, __________, and __________ are
in a line.
4. High tides happen every __________ hours.
5. The Moon takes about __________ days to orbit the Earth.
6. A __________ tide has the lowest water level.
7. Coastal areas may flood during __________ tides.
8. Scientists can use tides to generate __________.

🔸 D. Short Answer (8 Questions)

1. What is a tide?
2. What causes the ocean to rise and fall every day?
3. What is meant by “tidal force”?
4. How does the position of the Moon affect the tides?
 5. Why are tidal ranges larger during full or new moons?
6. How do tides affect harbours and shipping?
7. What is tidal energy, and how can it be used?
8. Name one natural hazard that is linked to tides.

Unit 3.5 & 3.6 – Energy and Changes in Energy

✅ Key Theory Summary

1. What is Energy?

 Energy is needed to do things – to move, heat, make sound or light, etc.

 Energy can be stored or transferred.
 The unit of energy is the joule (J).

2. Types of Energy Stores and Transfers

Energy Type Description Store/Transfer

Thermal Heat energy in hot objects Store or transfer
Kinetic Energy from movement Store
Chemical In food, fuel, batteries Store
Gravitational Potential In objects lifted against gravity Store
Elastic Potential In stretched or squashed objects Store
Electrical Flow of electric current Transfer
Light Visible energy from luminous objects Transfer
Sound From vibrating objects Transfer

Example: A moving bus uses chemical energy from fuel, which transfers into kinetic,
thermal, sound, and light energy.

3. How Energy Changes

 Energy is transformed from one form to another.

 Example: Chemical → Thermal → Kinetic (as in a power station).
 These transformations are called energy changes.
4. Useful and Wasted Energy

 Useful energy: energy that does what we want (e.g. light from a bulb).
 Wasted energy: usually thermal or sound energy that spreads out.
 Dissipated energy is wasted and cannot be recovered.

5. Examples of Energy Changes

 A fire: Chemical → Thermal + Light

 TV: Electrical → Sound + Light
 Book falling: Gravitational Potential → Kinetic
 Climbing stairs: Chemical → Kinetic → Gravitational Potential

🧠 Practice Exercises – Units 3.5 & 3.6

🔹 A. Multiple Choice (8 Questions)

1. What is the unit of energy?

A. Volt
B. Ampere
C. Newton
D. Joule
2. Which type of energy is stored in food and fuel?
A. Thermal
B. Kinetic
C. Chemical
D. Light
3. What kind of energy does a moving car have?
A. Sound
B. Kinetic
C. Elastic
D. Light
 4. Which of the following is a form of transferred energy?
A. Gravitational
B. Elastic
C. Electrical
D. Chemical
5. What happens when energy is transferred but not used?
A. It becomes more useful
B. It is stored
C. It is wasted
D. It disappears
6. What type of energy does a stretched spring store?
A. Sound
B. Elastic potential
C. Light
D. Gravitational
7. In a power station, chemical energy is changed into:
A. Light energy
B. Electrical energy
C. Kinetic energy only
D. Magnetic energy
8. Which process shows chemical → thermal energy?
A. Riding a bike
B. Using a battery
C. Burning wood
D. Dropping a ball

🔸 B. True / False (8 Questions)

1. Energy cannot be created or destroyed – only changed.

2. Sound energy is always useful.
3. The energy in a moving object is called kinetic energy.
4. Batteries store chemical energy.
5. A ball at the top of a hill has kinetic energy.
6. Wasted energy can always be reused.
7. Elastic potential energy is found in stretched rubber bands.
8. Light bulbs can waste energy as heat.

🔹 C. Fill in the Blank (8 Questions)

 1. The unit used to measure energy is the __________.
2. __________ energy is stored in fuel and batteries.
3. A car moving down the road has __________ energy.
4. Heat energy is also called __________ energy.
5. Sound and heat that spread out and cannot be reused are called __________
energy.
6. When energy changes, some of it is often __________.
7. __________ energy is stored when an object is lifted up.
8. A __________ helps us represent energy changes clearly.

🔸 D. Short Answer (8 Questions)

1. What is energy?
2. Give two examples of stored energy.
3. Describe a situation where energy is changed from chemical to thermal.
4. What is wasted energy?
5. Why is dissipated energy a problem?
6. Explain how energy is used when walking up stairs.
7. What is meant by an energy transfer?
8. Give one example of an energy change in a household appliance.

Unit 3.7 – Where Does Energy Go?

Key Theory Summary

1. Energy Change and Transfer

 When energy is used, it is transferred or changed into other forms.

 Some of this energy is useful, and some is wasted.

2. Useful vs. Wasted Energy

 Useful energy: transferred into a form we want (e.g. kinetic energy to move a
vehicle).
 Wasted energy: often becomes thermal energy or sound, which spreads out and
can’t be recovered.
 Wasted energy is said to be dissipated and cannot be recovered.

3. Efficiency Examples
  Motorcycles use chemical energy from fuel, but only ~25% is converted into
useful motion. The rest becomes wasted thermal and sound energy.
 Light bulbs:
o Lamp A: only 15% useful (light); 85% is wasted as heat.
o Lamp B: 50% useful (light); 50% wasted.

4. Energy in Heating

 Some thermal energy is lost to surroundings (e.g. air, rocks, steam).

 Not all energy from a source (like fire) gets transferred into the target (e.g. water).

Practice Exercises – Unit 3.7

A. Multiple Choice (8 questions)

1. What does “dissipated energy” mean?

A. Energy used efficiently
B. Energy that can be recovered
C. Energy that spreads out and is wasted
D. Energy that becomes stronger
2. Which is an example of wasted energy in a motorcycle?
A. Movement
B. Fuel
C. Light
D. Heat and sound
3. What percentage of energy in fuel is used for movement in a motorcycle?
A. 100%
B. 75%
C. 25%
D. 5%
4. Why is thermal energy called “wasted energy” in many cases?
A. It cannot move
B. It is useful
C. It escapes and cannot be used
D. It turns into light
 5. Which lamp is more efficient?
A. Lamp A (15% light, 85% heat)
B. Lamp B (50% light, 50% heat)
6. What kind of energy is used to boil water over a fire?
A. Chemical to light
B. Chemical to thermal
C. Light to sound
D. Sound to movement
7. What energy change happens when walking up stairs?
A. Kinetic → chemical
B. Chemical → gravitational potential
C. Light → chemical
D. Thermal → kinetic
8. What is true about wasted energy?
A. It helps machines work better
B. It is always thermal
C. It cannot be recovered
D. It is stored for later use

B. True / False (8 questions)

1. Wasted energy can be recovered later.

2. Thermal energy is often the main type of wasted energy.
3. All energy used in a car is turned into movement.
4. Light bulbs can waste energy as heat.
5. Dissipated energy is energy that spreads out.
6. Energy can be changed from one form to another.
7. The fire transfers all thermal energy into water.
8. Sound is always a useful energy form.

C. Fill in the Blank (8 questions)

1. When energy spreads out and cannot be reused, it is called __________.

2. Useful energy is the energy that does what we __________.
3. In a motorcycle, most of the chemical energy becomes __________ and sound.
4. A light bulb wastes energy as __________.
5. Some of the fire’s energy is lost to the __________ around it.
6. Energy that is wasted cannot be __________.
7. Energy that is useful helps us do __________.
8. Lamp B is more __________ than Lamp A.