2.8 gravity
TRANSCRIPT
Chapter 2 Forces and Motion
2.8 Gravity
2.8 Gravity
2.8 GravityAccording to Newton, objects fall because they are pulled towards the Earth by the
force of gravity.
2.8 GravityThe pull of gravitational force;
(a)keeps things on the earth. (b)brings things down to earth when
they are thrown upwards (c)holds the moon in its orbit round
the Earth (d)captures returning space capsules
and pulls them into orbit.
2.8 GravityThe pull of gravity causes objects
to fall with acceleration.
This means that objects that fall are moving with increasing velocity.
2.8 GravityThe magnitude of the acceleration
due to gravity depends on the strength of the gravitational field.
The gravitational field is the region around the Earth in which an object experiences a force towards the centre of the Earth.
Earth’s gravitational field strength, g, is about 9.8 N kg-1
2.8 GravityFree Fall
An object is falling freely when it is falling
under the force of gravity only.
(No air resistance)
2.8 Gravity
Free fall in vacuum
Not a free fall in air due to
air resistance
2.8 Gravity
• When an object falls, g = 9.8 m s-2
• When an object is thrown upwards,
g = - 9.8 m s-2
• At the highest point, v = 0
2.8 GravityObjects dropped under the influence of the
pull of gravity accelerate at a constant rate.
This acceleration is known as the gravitational acceleration, g.
The value of g is 9.8 m s-2. In calculation, the value of g is often taken to be 10 m s-2
for simplicity. The acceleration due to gravity does not
depend on the mass and shape of the falling object.
All objects falling freely with the same acceleration.
2.8 Gravity
Weight and Mass
2.8 GravityWeight (W) and Mass
(m)
2.8 GravityWeight (W) and Mass
(m)
2.8 GravityWeight (W) and Mass
(m)
2.8 GravityWeight (W) and Mass
(m)
2.8 GravityWeight (W) and Mass
(m)
2.8 GravityWeight (W) and Mass
(m)
2.8 GravityWeight (W) and Mass
(m)
Your weight in an elevator!!!
2.8 GravityWeight (W) and Mass
(m)Your mass = 50 kg
2.8 GravityWeight (W) and Mass
(m)Your mass = 50 kg
Acceleration = a
You feel HEAVIER!
2.8 GravityWeight (W) and Mass
(m)Your mass = 50 kg
2.8 GravityWeight (W) and Mass
(m)Your mass = 50 kg
You feel LIGHTER!
2.8 GravityWeight (W) and Mass
(m)
• http://www.batesville.k12.in.us/physics/phynet/mechanics/newton2/ElevatorProblem.html
• http://education-portal.com/academy/lesson/newtons-laws-and-weight-mass-gravity.html#lesson
1. Subra is standing on a weighing scale inside an elevator. If Subra’s mass is 63kg, find the reading of the weighing scale when the lift,
a. stationaryb. moving upward with a constant velocity,
15 ms-1.,c. moving upward with a constant acceleration,
1 ms-2.d. moving downward with a constant
acceleration, 2 ms-2.[use g = 10 m/s^2]
(a) W = mg = 63(10) = 630 N(b) W = mg = 63(10) = 630 N(c) R = mg + ma = 63(10)+63(1) = 693 N(d) R = mg - ma = 63(10)-63(2) = 504 N
