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# Ch.14.forces and motion (week 2)

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Magnetic force, weight and gravitational force

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### Ch.14.forces and motion (week 2)

1. 1. FORCES AND MOTION Physics Chapter 14. (Week 2)
2. 2. NON- CONTACT FORCES Magnetic forces Electrostatic Forces Gravitational forces
3. 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. 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. 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. 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. 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. 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.