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# Physics On the Road - Lesson 11

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### Physics On the Road - Lesson 11

1. 1. 9/15/2013 1 The Gravity Field Physics on the Road Lesson 11
2. 2. 9/15/2013 2 LI…  Explain the difference between mass and weight  Know that the weight of an object is proportional to it’s mass  Describe a gravitational field
3. 3. 9/15/2013 3 Newton’s 3 Ideas  Mass and weight  The gravity field  Forces change velocities
4. 4. 9/15/2013 4 Mass and weight: on Earth, on the Moon  The force needed to push the sack is related to it’s mass and resistance to this is called inertia.  The force needed to lift the sack is related to it’s mass and called it’s weight.  Would there be difference on the moon?
5. 5. 9/15/2013 5 Mass and weight  The pull of gravity on an object is proportional to it’s mass and is called it’s weight. weight = mass x gravity  The force needed to accelerate an object is proportional to it’s mass force = mass x acceleration  The weight of an object is a force and has units of Newtons (N)  Mass is the amount of matter and has units of kilograms (kg) W = mg F = ma Gravity and acceleration are equivalent
6. 6. 9/15/2013 6 The Gravity Field  In physics we use the idea of invisible regions or fields filling space to explain forces which act at a distance (non- contact)  Gravity (or weight) is a non-contact force and is produced by a gravity field  Newton’s famous idea was that masses produce their own gravity fields. The bigger the mass the stronger the field. planet Planet surface
7. 7. 9/15/2013 7 Gravity and acceleration  W = mg and F = ma are equivalent formulas (because weight is a force)  So this means that for objects in a gravity field the field and the objects acceleration are equivalent. So gravity fields have two units 1. Newtons/kilogram - Nkg-1 2. Metres/second/second - ms-2 F = mg and a = F / m So for either mass… acceleration = mg / m = g ie. they fall with same acceleration. W w gravity field
8. 8. 9/15/2013 8 Forces change velocities  Newton explained that forces change velocities.  Sometimes this means a change of speed, but not always. 1. Use the ideas of vectors to explain that a change of velocity can happen without a change of speed 2. Give an astronomical example of this and use a diagram 3. Isaac Newtons ideas were slow to be accepted in the 17th Century (particularly in France). Use the differences in transport between then and now to explain why.