Transcript 6. falling objects

Mass and Weight
Mass
This is the amount of matter.
(Kg)
Weight This is the force of gravity pulling on the mass.
* less on the moon , zero in deep space.
There is a very, small force
of attraction between
an apple and an orange.
* too small to measure!
(N)
Weight vs. Mass
Earth’s Gravitational Field Strength is 10N/kg. In other
words, a 1kg mass is pulled downwards by a force of 10N.
W
Weight = Mass x Gravitational Field Strength
(in N)
(in kg)
(in N/kg)
M
g
1) What is the weight on Earth of a book with mass 2kg?
2) What is the weight on Earth of an apple with mass 100g?
3) Dave weighs 700N. What is his mass?
4) On the moon the gravitational field strength is 1.6N/kg. What will
Dave weigh if he stands on the moon?
Forces on falling objects
1. Object falling freely
Forces Acting
Motion
Forces on falling objects
1. Object falling freely
Forces Acting
the force of gravity
(weight)
Motion
Uniform acceleration
Forces on falling objects
1. Object falling freely
Forces Acting
the force of gravity
(weight)
Motion
Uniform acceleration
Forces on falling objects
1. Object falling freely
Forces Acting
the force of gravity
(weight)
Motion
Uniform acceleration
Object in air
Forces on falling objects
1. Object falling freely
Forces Acting
the force of gravity
(weight)
Motion
Uniform acceleration
Object in air
Forces on falling objects
1. Object falling freely
Forces Acting
the force of gravity
(weight)
Motion
Uniform acceleration
( …….. m/s/s)
Object in air
acceln = gradient
Forces on falling objects
1. Object falling freely
Forces Acting
the force of gravity
(weight)
Motion
Uniform acceleration
( …….. m/s/s)
Object in air
acceln = gradient
Forces on falling objects
1. Object falling freely
Forces Acting
the force of gravity
(weight)
Motion
Uniform acceleration
(10 m/s/s)
Object in air
Forces on falling objects
1. Object falling freely
Forces Acting
the force of gravity
(weight)
Motion
Uniform acceleration
(10 m/s/s)
If a 1kg mass is released above the ground
* the force of gravity on it is 10N
* its acceleration is force = 10N =10m/s/s
mass 1Kg
2. Object falling through a fluid
Forces Acting
force of gravity (weight)
Motion
* initial acceleration (10 m/s/s)
*
*
Object in air
2. Object falling through a fluid
Forces Acting
Motion
force of gravity (weight)
* initial acceleration (10 m/s/s)
Drag force (air resistance) * decreasing acceleration to zero
* terminal velocity
Buoyancy (upthrust)
Object in air
2. Object falling through a fluid
Forces Acting
Motion
force of gravity (weight)
* initial acceleration (10 m/s/s)
Drag force (air resistance) * decreasing acceleration to zero
* terminal velocity
Buoyancy (upthrust)
Object in air
Terminal Velocity
Consider a skydiver:
1) At the start of his jump the air
resistance is _______ so he
_______ downwards.
Terminal Velocity
Consider a skydiver:
1) At the start of his jump the air
resistance is _______ so he
_______ downwards.
2) As his speed increases his air
resistance will _______
Terminal Velocity
Consider a skydiver:
1) At the start of his jump the air
resistance is _______ so he
_______ downwards.
2) As his speed increases his air
resistance will _______
3) Eventually the air resistance will be
big enough to _______ the
skydiver’s weight. At this point
the forces are balanced so his
speed becomes ________ - this is
called TERMINAL VELOCITY
Terminal Velocity
Consider a skydiver:
4) When he opens his parachute the
air resistance suddenly ________,
causing him to start _____ ____.
5) Because he is slowing down his air
resistance will _______ again until
it balances his _________. The
skydiver has now reached a new,
lower ________ _______.
Velocity-time graph for terminal velocity…
Parachute opens –
diver slows down
Velocity
Speed
increases…
Terminal
velocity
reached…
Time
New, lower terminal
velocity reached
Diver hits the ground
less than
equal to
equal to