gravity and free fall (3)
TRANSCRIPT
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 1/23
To-Do:
Grab a study guide from the side counter andcut it in ½ to share with a partner.
Do Not paste it in your journal
In your whirligig groups, discuss the “ScienceBehind It” column in your Deep Dive journalnotes.
Discuss topics such as Gravity, Air Resistance, Mass,Force, Surface Area, Etc.
Complete the right hand side of your notes foreach conclusion that you wrote.
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 2/23
Gravity, Air Resistance,
Terminal Velocity, andProjectile Motion
A Whole Bunch of Ideas in one Show
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 3/23
By the end of this presentation,
you should be able to: Describe and explain what is meant by
terminal velocity.
Describe and explain how forces changeon a falling object.
Recall and explain the meanings of the
terms „stopping distance‟, „thinkingdistance‟ and „braking distance‟ and thefactors which affect them.
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 4/23
What is a force
Push or pull
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 5/23
Some basics…
Newton‟s second law states thatincreasing mass will ____________
the acceleration. Friction always acts in the _________
direction as motion.
When an object is thrown upward, thenet force will be the result of theinteractions between the upward forceand __________.
decrease
opposite
gravity
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 6/23
What IS gravity?
Gravity is NOT “the force that pullsyou down!”
Gravity attracts all objects with massto all other objects with mass.
Why?... Who knows!
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 7/23
the Force of Gravity
What is the force of gravity?
The force of gravity is NOT the same
as the acceleration DUE to gravity!
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 8/23
Free Fall
Objects whose only acceleration is dueto gravity are in free fall.
Theoretically, objects in free fallcontinue to accelerate as long as theyare falling.
All free falling objects accelerateat the same rate regardless of their mass.
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 9/23
Galileo's Famous
Experiment
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 10/23
Acceleration of Gravity
Any object which is beingacted upon only by theforce of gravity is said tobe in a state of free fall.There are two importantmotion characteristicswhich are true of free-falling objects: – Free-falling objects do
not encounter airresistance. – All free-falling objects
(on Earth) acceleratedownwards at a rate of 9.8 m/s/s (often
approximated as 10m/s/s)
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 11/23
If the velocity and time for a free-falling objectbeing dropped from a position of rest weretabulated, then one would note the following
pattern. Time (s) Velocity (m/s)
0 0
1 - 9.8
2 - 19.6 3 - 29.4
4 - 39.2
5 - 49.0
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 12/23
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 13/23
Free Fall
Newton‟s 2nd Lawpredicts this!
a = Fm
The force of gravityfelt by a moremassive object is
greater
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 14/23
Air Resistance
Air resistance is an upward forceexerted on an object as it falls by air
It is, in essence, a frictional force For simplicity, the amount of air
resistance is determined by two
factors – The cross-sectional area of the object
– The speed of the object
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 15/23
Terminal VelocityDetermine the acceleration of this 85 kg skydiver at points A-D.
9.8 m/s2 5.68 m/s2 1.56 m/s2 0 m/s2
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 16/23
Terminal Velocity
The terminal velocity of a skydiver in afree-fall position with a semi-closed
parachute is about 195 km/h Higher speeds can be attained if the
skydiver pulls in his limbs. In this case,
the terminal velocity increases toabout 320 km/h!
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 17/23
The more compact anddense the object, thehigher its terminal
velocity will be. Typicalexamples are the
following: raindrop,25 ft/s, a skydiver wasfound to be in a range
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 18/23
By the end of this presentation, you should beable to:
Describe and explain what is meant byterminal velocity.
Describe and explain how forces change on afalling object.
Recall and explain the meanings of the terms
„stopping distance‟, „thinking distance‟ and „braking distance‟ and the factors which affectthem.
W Ri h ds W thi Hi h S h l
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 19/23
Terminal VelocityConsider a skydiver:
1) At the start of his jump the airresistance is _______ so he
____ downwards.
2) As his speed increases his airresistance will _______
3) Eventually the air resistance will be
big enough to _______ theskydiver’s weight. At this pointthe forces are balanced so hisspeed becomes ________ - this iscalled TERMINAL VELOCITY
zero
accelerates
increase
balance
constant
W Richards Worthing High School
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 20/23
How the forces change with time.
KEY
Weight (constant value and
always present)
Air resistance(proportional to thespeed)
Resultant force
(the bigger theunbalanced force the
greater theacceleration)
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 21/23
Terminal
VelocityConsider a skydiver:
4) When he opens his parachute theair resistance suddenly ________,causing him to start _____ ____.
5) Because he is slowing down his airresistance will _______ until it
balances his _________. Theskydiver has now reached a new,lower ________ _______.
increasesslowing down
decrease
weight
terminal velocity
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 22/23
Velocity-time graph for thesky diverVelocity
Time
Speedincreases…
Terminal
velocityreached…
Parachute opens – diver slows down
New, lower terminalvelocity reached
Diver hits the ground
7/27/2019 Gravity and Free Fall (3)
http://slidepdf.com/reader/full/gravity-and-free-fall-3 23/23
Projectile Motion
Projectile: When afalling object also
experienceshorizontal motion
Horizontal motiondoes not affect
vertical motion