Hard and Soft — Physics (Grade 7)

Define and explain Hard and Soft in your own words
Use key terms such as property accurately
Apply what you have learned to new examples and questions
Avoid the common mistakes learners make with this topic

Everything around you is made from materials — wood, metal, plastic, glass, fabric and more. Each material has special properties that make it perfect for some jobs and useless for others. In this chapter you will become a materials detective.

This lesson focuses on Hard and Soft: feeling and comparing materials by how hard or soft they are.

Definition: Hard and Soft

Feeling and comparing materials by how hard or soft they are.

Key ideas

Materials have properties we can feel and see

Run your hand over sandpaper and silk and the difference is obvious: rough versus smooth. Properties like hardness, shininess and flexibility help us describe materials precisely. Scientists group materials by these properties to decide what each one is good for.

We choose materials to suit the job

Wellies are made of rubber because rubber is waterproof and bendy. Windows are made of glass because it is transparent and hard. Matching the property to the purpose is the key idea behind materials science, and engineers do it for everything from bridges to lunchboxes.

Key term — property: Something you can observe about a material, such as whether it is hard, soft, shiny, rough or bendy.

Worked example: Hard and Soft

Is a wooden spoon hard or soft? How could you test it?

Hard — you cannot dent it with a fingernail or bend it easily.

Answer: Hard — you cannot dent it with a fingernail or bend it easily.

Common mistakes

Saying 'material' when you mean 'object' The object is the chair; the material is the wood it is made from.
Thinking glass is always transparent Frosted or stained glass is translucent — it lets some light through but you cannot see clearly through it.

Practice

Give one property that makes metal good for saucepans.

Think about heat.

Metal conducts heat well, so heat from the cooker spreads quickly through the pan. It is also strong and hard.

Sort these into natural and man-made materials: wood, plastic, cotton, glass.

Natural materials come from plants, animals or rocks.

Natural: wood, cotton. Man-made: plastic, glass.

Name one transparent material and one opaque material.

Think of windows and walls.

Transparent: glass or clear plastic. Opaque: wood, metal or brick.

A material lets some light through but you cannot see through it clearly. What word describes it?

It sits between transparent and opaque.

Translucent.

Quick check

Hard and Soft — quick check

Which of these best defines "property"?

Something you can observe about a material, such as whether it is hard, soft, shiny, rough or bendy.

Why are umbrellas not made of paper?

Paper is not waterproof — it soaks up water and tears, so it would fail as an umbrella.

Key takeaways

Hard and Soft: feeling and comparing materials by how hard or soft they are.
Materials have properties we can feel and see: Run your hand over sandpaper and silk and the difference is obvious: rough versus smooth.
material: What something is made from, such as wood, metal, plastic, glass, fabric or rock.
Watch out for: saying 'material' when you mean 'object'

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