Physics Beginner

Matter is everything that takes up space and has weight. Your desk, the air you breathe, and the water in your glass are all matter. Scientists group matter into three main states: solid, liquid, and gas.

• Solids keep their own shape — a rock, a book, an ice cube.
• Liquids take the shape of their container — water, juice, honey.
• Gases spread out to fill all available space — air, steam, helium in a balloon.

You can change the state of matter by heating or cooling it. Ice (solid) melts into water (liquid) when it warms up. Water turns into steam (gas) when it boils.

Ice  →(heat)→  Water  →(more heat)→  Steam
Solid           Liquid                Gas

A force is a push or a pull. Forces can make objects start moving, stop moving, speed up, slow down, or change direction. You cannot see a force, but you can see what it does.

• Kicking a ball is a push.
• Opening a door towards you is a pull.
• Forces are measured in units called newtons (N).

When two equal forces push in opposite directions, they balance and nothing moves. When forces are unbalanced, the object moves in the direction of the bigger force.

← 5 N   |   5 N →   balanced — object stays still
← 3 N   |   7 N →   unbalanced — object moves right

Gravity is a pulling force that every object with mass has. The Earth is very large, so its gravity pulls everything towards its centre. That is why objects fall down when you drop them.

• Gravity keeps us on the ground and holds the Moon in orbit around Earth.
• A heavier object and a lighter object dropped from the same height hit the ground at almost the same time (ignoring air resistance).
• On the Moon gravity is weaker, so you would weigh less there, even though your mass stays the same.

Weight is the force of gravity pulling on an object. Mass is the amount of matter in an object. They are different!

Friction is a force that acts between two surfaces that rub together. It opposes motion — it tries to slow things down or stop them from sliding.

• Rough surfaces (sandpaper, carpet) create more friction.
• Smooth surfaces (ice, polished marble) create less friction.
• Friction can be useful: it lets you walk without slipping, helps car tyres grip the road, and lets brakes slow a bicycle.
• Friction can be a problem: it wears out shoe soles and slows machines down. Oil or grease can reduce it.

High friction → harder to slide (rough surfaces)
Low friction  → easier to slide (smooth or oily surfaces)

A magnet is an object that produces an invisible force that can attract (pull towards) or repel (push away) certain metals, especially iron and steel.

• Every magnet has two poles: a north (N) pole and a south (S) pole.
• Opposite poles attract: N attracts S.
• Like poles repel: N pushes away N, and S pushes away S.
• Magnets attract iron, steel, nickel, and cobalt — but not plastic, wood, or aluminium.
• The Earth itself acts like a giant magnet, which is why compass needles point north.

N — S  (attract, they pull together)
N — N  (repel, they push apart)
S — S  (repel, they push apart)

Light travels in straight lines from a source. The Sun is our biggest source of natural light. Other sources include torches, candles, and light bulbs.

• Transparent objects (like glass or clear water) let most light through.
• Translucent objects (like tissue paper) let some light through but scatter it.
• Opaque objects (like wood or metal) block light completely and create a shadow.

A shadow forms on the side of an opaque object that is away from the light source. Shadows change size: move an object closer to a light source and the shadow grows bigger; move it further away and the shadow shrinks.

Light source → [opaque object] → shadow on the other side

Sound is created when something vibrates — moves back and forth very quickly. Those vibrations travel through the air as waves and reach your ears.

• Pluck a guitar string and feel it vibrate — that vibration makes the sound you hear.
• Sound can travel through solids, liquids, and gases, but it cannot travel through empty space (a vacuum).
• Sound travels faster through solids than through air.
• Loud sounds come from bigger vibrations; soft sounds come from smaller vibrations.
• High-pitched sounds come from fast vibrations; low-pitched sounds come from slow vibrations.

Fast vibration  → high pitch (e.g. whistle)
Slow vibration  → low pitch  (e.g. bass drum)

Temperature tells us how hot or cold something is. We measure it in degrees Celsius (°C) using a thermometer.

• Water freezes at 0 °C and boils at 100 °C at sea level.
• Normal body temperature is about 37 °C.
• Heat always flows from a hotter object to a cooler one — never the other way on its own.
• When you hold an ice cube, heat from your hand flows into the ice, making your hand feel cold.

Temperature and heat are different things. Temperature measures how hot something is; heat is the energy that flows from hot to cold.

0 °C   — water freezes (ice)
37 °C  — human body temperature
100 °C — water boils (steam)

Simple machines make work easier — they let you use less force or move things more easily. There are six classic simple machines; here are four important ones:

• Lever: a stiff bar that pivots on a point called the fulcrum. A see-saw is a lever. A crowbar helps lift heavy rocks.
• Inclined plane (ramp): a sloped surface. It takes less force to push a box up a ramp than to lift it straight up.
• Wheel and axle: a wheel attached to a rod. A door knob, bicycle wheel, and rolling suitcase all use this idea.
• Pulley: a wheel with a rope over it. Pulling down on one end of the rope lifts a load on the other end. Cranes use pulleys.

Lever:  -------●-------  (● = fulcrum)
Ramp:   push along slope  is easier than lifting straight up

Whether an object floats or sinks in water depends on its density compared with water. Density means how much matter is packed into a given space.

• Objects less dense than water float — wood, a plastic bottle, a rubber duck.
• Objects more dense than water sink — a stone, a coin, a metal spoon.
• Shape matters too: a solid ball of steel sinks, but the same steel shaped into a hollow bowl can float because the air inside lowers the overall density.
• That is how large steel ships float!

Water pushes upward on anything placed in it — this upward push is called the buoyant force. If the buoyant force is large enough, the object floats.

The Earth is a planet that travels around the Sun. The Moon travels around the Earth. Understanding their movements explains day and night and the phases of the Moon.

• The Earth spins on its axis once every 24 hours. The side facing the Sun has day; the side facing away has night.
• The Earth takes about 365 days (one year) to orbit the Sun.
• The Moon takes about 28 days (one month) to orbit the Earth.
• The Moon does not produce its own light — it reflects light from the Sun.
• Stars are like the Sun but very far away — they appear small because of the distance.

Sun → light → Earth (day side) / shadow side (night)
Moon orbits Earth and reflects sunlight → moonlight