The Force Family

Why it matters

A cricket bat must TOUCH the ball. The Earth pulls the same ball from a hundred metres away without touching anything. Two families of force, one physics.

The idea in plain words

The force census. Tap the families.

contact · non-contact

A book rests on a table. Name the two forces on it.

They balance — the book stays put

• family 1: contact — friction, normal reaction, tension — delivered by touching surfaces
• family 2: non-contact — gravitational, magnetic, electrostatic — fields acting at a distance
• measuring force: unit — the newton (N); 1 kgf = 9.8 N (the gravitational unit)
• Earth pulls it down: weight (non-contact)
• Table pushes it up: normal reaction (contact)

Predict first

Which force acts WITHOUT contact?

Gravity, magnetism and electrostatic attraction reach across empty space — the non-contact family. Friction, normal reaction and tension need surfaces meeting.

• the gravitational pull on a falling mango — correct
• friction on a sliding book
• the tension in a kite string

What you do

Sort the six forces into their families.

Check yourself

1 kgf equals about…

kgf is the pull of gravity on 1 kg — g newtons, ≈ 9.8 N.

The force a table exerts UP on a resting book is called…

Normal = perpendicular to the surface. Friction acts ALONG the surface, only when sliding threatens.

Which is a non-contact force pair?

Magnets and charged combs act across air gaps — no touching required.

• 9.8 N — correct
• 1 N
• 98 N
• normal reaction — correct
• friction
• tension
• magnetic and electrostatic — correct
• friction and tension
• normal reaction and friction