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# Mass & weight

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### Mass & weight

1. 1. What is gravity?
2. 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. 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. 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. 5. The size of the force also depends on thedistance between the objects.
6. 6. We only really notice the gravitationalattraction to big objects! Hola! ¿Como estas?
7. 7. The force of gravity on something is called itsweight. Because it is a force it is measured inNewtons. Weight
8. 8. On the earth, Mr Porter’s weight is around 800 N. I love physics! 800 N
9. 9. On the moon, his weight is around 130 N.Why? 130 N
10. 10. In deep space, far away from any planets or stars his weight is almost zero. (He is weightless). Why? Cool!
11. 11. Mass is a measure of the amount of materialan object is made of. It is measured inkilograms.
12. 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. 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. 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. 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. 16. Calculating weightThe force of gravity on one kilogram is calledthe gravitational field strength. It s measuredin Newtons per kilogram (N/kg)
17. 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. 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. 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. 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. 21. Easy isn’t it?