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- 1. What is gravity?
- 2. • Gravity is the force that pulls all objects in the universe toward one another.• Gravity is the force which pulls all objects to the surface.
- 3. Gravity is a very weak force. The force of gravitational attraction between Mr Porter and his wife (when 1 metre apart) is only around 0.0000004 Newtons!
- 4. The size of the force depends on the mass of the objects. The bigger they are, the bigger the force!Small attractive force Bigger attractive force
- 5. The size of the force also depends on thedistance between the objects.
- 6. We only really notice the gravitationalattraction to big objects! Hola! ¿Como estas?
- 7. The force of gravity on something is called itsweight. Because it is a force it is measured inNewtons. Weight
- 8. On the earth, Mr Porter’s weight is around 800 N. I love physics! 800 N
- 9. On the moon, his weight is around 130 N.Why? 130 N
- 10. In deep space, far away from any planets or stars his weight is almost zero. (He is weightless). Why? Cool!
- 11. Mass is a measure of the amount of materialan object is made of. It is measured inkilograms.
- 12. Mr Porter has a mass of around 77 kg. Thismeans he is made of 77 kg of blood, bones,hair and poo! 77kg
- 13. On the moon, Mr Porter hasn’t changed (he’sstill Mr Porter!). That means he still is made of77 kg of blood, bones, hair and poo! 77kg
- 14. In deep space, Mr Porter still hasn’t changed(he’s still Mr Porter!). That means he still ismade of 77 kg of blood, bones, hair and poo! I feel sick! 77kg
- 15. Mass is a measure of the amount of materialan object is made of. It is measured inkilograms.Weight is the force of gravity on an object. It ismeasured in Newtons.
- 16. Calculating weightThe force of gravity on one kilogram is calledthe gravitational field strength. It s measuredin Newtons per kilogram (N/kg)
- 17. • Force = Mass x Acceleration • Force is measured in Newtons ACCELERATION of GRAVITY(Earth) = 9.8 m/s2 • Weight (force) = mass x gravity (Earth) Moon’s gravity is 1/6 of the Earth’sIf you weigh 420 Newtons on earth, what will you weighon the Moon? 70 Newtons If your mass is 41.5Kg on Earth what is your mass on the Moon?
- 18. Calculating weightTo calculate the weight of an object you multiplythe object’s mass by the gravitational fieldstrength wherever you are. Weight (N) = mass (kg) x gravitational acceleration(m/s2)
- 19. Example The gravitational field strength on earth is around 10 N/kg. What is your weight if your mass is 45 kg?Weight (N) = mass (kg) x gravitational field strength (N/kg)Weight (N) = 45 kg x 10 N/kgWeight = 450 N
- 20. Newton’s Second Law One rock weighs 5 Newtons. The other rock weighs 0.5 Newtons. How much more force will be required to accelerate the first rock at the same rate as the second rock? Ten times as much
- 21. Easy isn’t it?

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