Is it essential for an object applying force on another object to always be in contact with it?
Answer
No, it is not. There are forces whose effect can be experienced even if the objects are not in contact. These are called non-contact forces.
Muscular force and friction need touching — they are contact forces. But a magnet pulls an iron nail across a gap, a rubbed comb lifts bits of paper without touching them, and the Earth pulls a falling mango although nothing joins the two. The three non-contact forces studied in this chapter are the magnetic force, the electrostatic force and the gravitational force.
Q2.
Can you recall that a magnet could exert force on another magnet or a magnetic material without being in contact with it?
Answer
Yes. We learnt this in the chapter ‘Exploring Magnets’ in Curiosity, Grade 6.
A magnet attracts objects made of magnetic materials, such as iron pins, without touching them.
When two magnets are brought close, like poles (North–North, South–South) repel each other and unlike poles (North–South) attract each other.
In an earlier chapter of this book we also learnt about electromagnets, which behave like magnets.
Attraction and repulsion are themselves a pull and a push — that is, a force. And the gap between the two magnets shows that this force does not need contact.
Q3.
Are there more such forces which act from a distance?
Answer
Yes — two more are studied in this chapter.
Non-contact force
Exerted by
Attractive or repulsive?
Magnetic force
A magnet, on another magnet or on a magnetic material
Either — like poles repel, unlike poles attract
Electrostatic force
A charged body, on another charged or uncharged body
Either — like charges repel, unlike charges attract
Gravitational force
The Earth (and every other planet), on every object