This document discusses three types of non-contact forces: magnetic forces, electrostatic forces, and gravitational forces. It provides details on magnetic forces and how opposite poles attract and similar poles repel. It also explains that gravitational forces act between any two masses in the universe, and the force is stronger between larger masses like the sun and earth. Finally, it defines the difference between mass and weight, where mass is the amount of matter and weight is the gravitational force acting on an object that can vary in different gravitational fields.

1. FORCES AND
MOTION
Physics
Chapter 14.
(Week 2)

2. NON- CONTACT FORCES
Magnetic
forces
Electrostatic
Forces
Gravitational
forces

3. MAGNETIC FORCE
 A magnet has a north pole and a south pole .
 If u bring two magnets and put their similar poles together, you will feel
a force pushing your hands apart as they repel , the strength of the push
increases as you bring the similar poles closer together .
 If you bring the opposite poles together, you will feel your hands being
pulled together as the different poles attract , the strength of the pull
increases as the poles get closer.
 A magnet can also exert a non contact – pulling force on iron , cobalt ,
steel or nickel.
 The strength of this force increases as the magnet and any of these
magnetic materials are brought closer together.

4. GRAVITATIONAL FORCE
 Is a force between any 2 masses in the universe.
 The masses may be small : such as an ant and a pebble .
 Or may be very large : such as the sun and the earth .
 The gravitational force between small masses is very weak to
have any effect on them.
 But the gravitational force between two large masses such as
the sun and the earth is large enough to be very important .
 The gravitational force between the sun and all the planets is
what holds the planets in their orbits.

5. MASS AND WEIGHT
 The gravitational force between an object on earth and the
earth itself pulls the object down towards the center of the
earth.
 This gravitational force is called the weight of the object .
 Mass : the measure of the amount of matter in an object.
 Weight : the pull of the earth’s gravity on an object .
 Example : an object may have a mass of 1 k.g , the pull of
earths gravity on 1 kg is a force of almost 10 newtons
 The weight of the 1 kg mass is therefore 10 N.

6. GRAVITATIONAL FIELD
 The region in which a force acts is called a field .
 there is a gravitational field around the earth .
 On earth the pull on a mass of 1 k.g is 10 N
 Therefore the gravitational field strength is10 N
 The gravitational field on mars is 3 times less than the
gravitational field on earth.
 Therefore a 1 k.g object that was 10 N on earth weights only
3.3 N on mars .
Gravitational field strength = weight / mass

7. ■ The Mass of an object never changes wherever it goes in the
universe but its Weight changes according to the gravitational
force that is acting upon it.

8.  The Mass of an object never changes wherever it goes in the
universe but its Weight changes according to the
gravitational force that is acting upon it.