Download Gravitational Field Strength & Satellites

Gravitational Field
Strength & Satellites
Gravitational Field Strength
Gravitational force per unit mass on
an object
g = Fg / m
(units = N/Kg)
 g = gravitational field strength
 Fg = Force of gravity (also weight)
 m = mass

Gravitational Field Strength
Example Problem:
While in orbit in the space shuttle, the
gravitational field strength on an
astronaut is 7.83 N/Kg.
1. How much does an 80 kg astronaut
weigh on the shuttle?
2. How much does the astronaut weigh
on Earth?

Gravitational Field Strength
Problem
How much does an 80 kg astronaut weigh on
the shuttle?
g = Fg / m (solve for Fg)
Fg = (7.83 N/Kg) x (80 Kg)
= 626.4 N (we don’t express in N)
= 626.4 N x .22 lbs/N
= 137.8 lbs
Gravitational Field Strength
Problem
How much does the astronaut weigh on
Earth?
Fg = (9.8 N/Kg) x (80 Kg)
= 784 N
= (784 N) x (.22 lbs/N)
= 172.5 lbs
Satellite Speed & Period
Remember, to solve for altitude you
must include the radius of the Earth
 To solve for altitude, use the equation
a = v2
(solve for “r”)
r
speed / velocity:
v = sqrt Gxm / r
period:
T = 2π x sqrt R3
GM

Satellite Speed & Period
When solving these problems, you
use the “M” – the large mass that the
satellite is revolving around
 “R” – the radius / altitude of the
satellite above the object it is orbiting
