Revision of JSS2 Lesson – JSS3 Intermediate Science Lesson Note (First Term)

Revision of JSS2 Intermediate Science is a review of mixtures, body systems, force and simple machines before the JSS3 topics begin.

Behavioural objectives

1. Define a mixture and name its two types with examples.
2. Describe how to separate mixtures by filtration, evaporation and sieving.
3. State the job of the skeletal, digestive, circulatory and respiratory systems.
4. Define force, state its effects and name its two types.
5. Name the six simple machines and give one example of each.

What is a mixture?

A mixture is a combination of two or more substances that are joined physically and do not form a new substance.

• No chemical change: each substance keeps its own properties.
• Easy to separate: simple physical methods can pull the parts apart.
• Any amount: the parts can be mixed in different proportions.

What are the types of mixture?

There are two types of mixture: homogeneous and heterogeneous.

Homogeneous mixture

• Meaning: it looks the same throughout, and you cannot see the separate parts.
• Example: sugar stirred into water. This is called a solution.
• Solute: the substance that dissolves (sugar).
• Solvent: the liquid that does the dissolving (water).

Heterogeneous mixture

• Meaning: the different parts can be seen easily.
• Examples: garri and groundnuts, oil floating on water, sand in water.

How do we separate mixtures?

Mixtures are separated by physical methods such as filtration, evaporation and sieving.

Steps in filtration

1. Place filter paper (or a clean cloth) in a funnel.
2. Pour the mixture into the funnel slowly.
3. The liquid (filtrate) passes through into a container.
4. The solid (residue) stays on the filter paper.

Steps in evaporation

1. Pour the salt solution into an evaporating dish.
2. Heat it gently.
3. The water changes to vapour and escapes.
4. The salt is left behind in the dish.

Steps in sieving

1. Pour the dry mixture onto a sieve (mesh).
2. Shake the sieve.
3. Small particles fall through the holes.
4. Large particles stay on top.

What are the body systems?

A body system is a group of organs that work together to do one main job that keeps us alive.

Skeletal system

• Job: gives the body its framework, support and shape.
• Bones: an adult human has 206 bones.
• Protection: the skull protects the brain, and the ribs protect the heart and lungs.

Digestive system

• Job: breaks down food such as yam, beans and rice into small nutrients.
• Nutrients: the blood carries them to the cells.
• Main parts: mouth, gullet, stomach, small intestine and large intestine.

Circulatory system

• Job: transports oxygen and digested food to every part of the body.
• Heart: pumps the blood.
• Blood vessels: tubes that carry the blood around the body.

Respiratory system

• Job: exchanges gases between the body and the air.
• Breathing in: we take in oxygen.
• Breathing out: we give out carbon dioxide.
• Main parts: nose, windpipe and lungs.

What is force?

A force is a push or a pull on an object, measured in newtons (N).

What can a force do?

• Start movement: it makes a stationary object move.
• Stop movement: it stops a moving object.
• Change direction: hitting a tennis ball sends it the other way.
• Change shape: squeezing a sponge changes its shape.

What are the types of force?

There are two types of force: contact force and non-contact force.

• Contact force: the object must be touched, as in pushing a desk.
• Non-contact force: acts from a distance, as in a magnet pulling a nail.
• Gravity: a non-contact force that pulls an apple to the ground.

What are simple machines?

A simple machine is a basic tool that makes work easier by reducing the effort needed.

What are the six types of simple machine?

The six simple machines are the lever, pulley, inclined plane, wheel and axle, screw and wedge.

What is mechanical advantage?

Mechanical advantage is a measure of how much a machine helps us.

• Formula: mechanical advantage = load ÷ effort.
• High value: a heavy load feels light, so the machine helps a lot.
• Unit: none, because it compares two forces.

Evaluation

1. Define a mixture and give one example of a solution.
2. Which method separates stones from sand, and which separates salt from salt solution?
3. Which body system handles breathing, and which handles food?
4. State two things a force can do to an object.
5. Name the six simple machines.

Assignment

List three simple machines found in your kitchen at home. For each one, name its type and say what job it does.