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Physics Chapter 9 - Gravity

Physics Chapter 9 - Gravity. Inverse-Square Law G Force Weightlessness. The Inverse-Square Law. Gravity decreases as the square of the distance increases (Inverse-Square Law) DISTANCE is measured between the centers of the objects!. Distance 1 2 3 4

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Physics Chapter 9 - Gravity

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  1. Physics Chapter 9 - Gravity Inverse-Square Law G Force Weightlessness

  2. The Inverse-Square Law • Gravity decreases as the square of the distance increases (Inverse-Square Law) • DISTANCE is measured between the centers of the objects! Distance 1 2 3 4 Force 1 1/4 1/9 1/16

  3. Inverse-Square Example The gravitational force between a 10,000 kg and a 20,000 kg asteroid separated by a distance of 100 meters is 1.33 x 10-6 N. What would the gravitational force be if the distance were somehow doubled to 200 m?

  4. G Force • Force on rides and in planes, etc are often compared to the normal force of gravity (weight) • The comparison is just a multiple of g (9.8 m/s2) • Example: “2 G’s” means the force you feel is due to acceleration being 2 x g, or in other words the force is 2 x your weight

  5. Gravity & Weightlessness • When weight is measured, something provides support (like the scale) so we aren’t falling • If you stand or sit on a scale in an elevator or on a ride at 6 Flags, your weight will vary (the force you feel)

  6. Gravity & Weightlessness • To feel weight, we need support. Weight is the force on (or by) the support • When falling, we don’t feel gravity because there is no support • If your inside something (car, elevator) that’s falling, you can’t weigh yourself or feel gravity!

  7. Weight & Weightlessness • Your weight equals the force with which you press against the supporting floor. • If the floor accelerates up or down, your weight varies (even though the gravitational force that acts on you remains the same)

  8. Gravity & Weightlessness • The moon and satellites are falling around the earth-–they are going fast enough not to crash into the earth • The earth and other planets are falling around the sun and when orbiting earth, astronauts are falling around earth! • The velocity needed to stay in orbit can be calculated (by using Potential and Kinetic Energy), which is called Escape Velocity and is about 11,200 m/s for earth

  9. Review Questions • Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that accelerated upward? Downward? • Give an example of when your weight is zero. • If the Earth somehow expanded to a larger radius, with no change in mass, how would your weigh be affected? How would it be affected if the Earth instead shrunk? (Hint: Let the equation for gravitational force guide your thinking.)

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