Universal Gravitation Physics. Warm-Ups WWhat is Newtonian Synthesis? SSame laws of physics that apply to Earth, also apply to the heavens.

Universal Gravitation

Physics

Warm-UpsWhat is Newtonian

Synthesis?Same laws of physics

that apply to Earth, also apply to the heavens

Warm-ups

A physics student has a mass of 70 kg and is separated from Earth by a distance of 6.60 x 106 m. What is the force of gravity between the physics student and Earth, if the mass of the Earth is 5.98 x 1024 kg?

686 N

Warm-Ups

Suppose that two objects attract each other with a gravitational force of 16 units. If the mass of both objects was doubled, and if the distance between the objects was doubled, then what would be the new force of attraction between the two objects?

It would not change

Warm-ups

If the mass of the moon is 7.34 x 1022 kg, the radius is 1.74 x 106 m, and G = 6.67 x 10-11 Nm2/kg2, what is g on the moon?

1.62 m/s2

Speed of an Object in Circular Orbit

V = √ Gm/r V : speed of object in orbit G : 6.67 x 10-11 Nm2/kg2

m : mass that the object is orbiting r : distance between two objects

(orbiting object and mass that it is orbiting)

Example Problem

If the mass of the sun is 2 x 1030 kg and the distance between mars and the sun is 2.28 x 1011 m, what is the orbiting speed of mars around the sun?

2.42 x 104 m/s

Period of Orbiting Object

T = 2*pi*r √r/Gmr : distance between 2

objectsG : 6.67 x 10-11 Nm2/kg2

m : mass that object is orbiting

Example Problem

For the previous example problem, find the orbiting period of mars around the sun.

5.9 x 107 s

Satellite Warm-UPThe mass of the Earth is

6 x 1024 kg and the radius of the Earth is 6.4 x 106 m. What is the value of g 1000 km above Earth?

7.31 m/s2

Weightlessness

Why do astronauts orbiting in space feel weightless?

Weightlessness

Astronaut and spaceship are free falling at the same rate of acceleration (g) and the normal force on the astronaut is 0

WeightlessnessHow does a spaceship stay

in orbit if it is free falling?Given a fast enough initial

velocity and misses the Earth because it is curved

Einstein’s Theory of Gravity

Gravity is not a force, but an effect of space itself

A mass causes space to be curved, an other masses are accelerated because of the way they follow this curved space

Einstein’s Theory of Gravity

Called General Theory of Relativity

During an eclipse, light was deflected by the sun, which provided evidence for this theory

Moon of Saturn Problem

Mimas, a moon of Saturn, has an orbital radius of 1.87 x 108 m and an orbital period of 23 hours (convert). Find the mass of Saturn.

5.65 x 1026

Gravitational Field StrengthGravitational force per

unit mass on an objectg = Fg/mUnits: Newton/kg

Gravitational Field Strength

Lines of forcedirectedinward

Gravitational Field Strength

The gravitational field strength is 7.83 N/kg at the altitude of the space shuttle. (a) How much does an 80 kg astronaut weigh on the shuttle? (b) How much did the astronaut weigh on earth? (1 N = .22 lbs.)

a) 137.8 lbb) 172.5 lb

Review for Quiz

Work in groups to finish back of review handout , pg. 188 (#6,7), and pg. 196 (#52)

Have me check off your paper when your group is done