Download What IS gravity?

STARTER
• Galileo Galilei was an Italian physicist, mathematician,
engineer, astronomer, and philosopher who played a
major role in the scientific revolution.
• He proposed that all falling bodies/objects accelerate
uniformly.
• Meaning if I dropped a bowling ball and a golf ball from
the rooftop they will hit the earth at the same time.
• Is this true? Why or why not?
GRAVITY, AIR RESISTANCE
AND TERMINAL VELOCITY
DAY 19
MINI-LAB
• Questions
• Pre-Lab Questions
1.If you drop the two objects from the same height, will
they hit the floor at the same time?
2.Does the mass or weight of the object have an effect on
how fast the object falls?
MINI-LAB
• Questions
• Post-Lab Questions
1.What does gravity mean to you?
2.Is gravity a weak force or a small force? Think before you
answer?
3.How do you know that there is gravity on Earth?
SOME BASICS…
DRAW A PICTURE ALONG WITH EACH FACT TO HELP YOU REMEMBER IT!
• An object’s mass _______
affect the acceleration of the
Won’t
object due to gravity on earth.
opposite
• Friction always acts in the _________
direction as motion.
surface area
• The ___________
of an object will affect the velocity of a
free falling object dropping towards earth.
WHAT IS GRAVITY?
• Gravity is NOT “the force that pulls you down!”
• Gravity attracts all objects with mass inward towards
other objects with mass.
THE FORCE OF GRAVITY
• What is the force of gravity?
• The force of gravity is NOT the same as the acceleration
DUE to gravity!
FREE FALL
• Objects whose only acceleration is due to gravity
are in free fall.
• Theoretically, objects in free fall continue to
accelerate as long as they are falling.
• All free falling objects accelerate at the same rate
regardless of their mass. (9.8 m/s2)
GALILEO'S FAMOUS EXPERIMENT
ACCELERATION OF GRAVITY
• Any object which is being acted upon
only by the force of gravity is said to be
in a state of free fall. There are two
important motion characteristics which
are true of free-falling objects:
• Free-falling objects do not
encounter air resistance.
• All free-falling objects (on Earth)
accelerate downwards at a rate of
9.8 m/s2 (often approximated as 10
m/s2)
FREE FALL
• Newton’s 2nd Law predicts
this!
•𝑎=
𝐹
𝑚
• The force of gravity felt by a
more massive object is
greater
AIR RESISTANCE
• Air resistance is an upward force exerted 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
TERMINAL VELOCITY
Determine the acceleration of this 85 kg skydiver at points A-D.
(Hint: F=ma)
9.8 m/s2
5.68 m/s2
1.56 m/s2
0 m/s2
TERMINAL VELOCITY
• The terminal velocity of a skydiver in a free-fall
position with a semi-closed parachute is about 195
km/hr.
• Higher speeds can be attained if the skydiver pulls
in his limbs. In this case, the terminal velocity
increases to about 320 km/hr!
• The more compact and dense the object, the higher
its terminal velocity will be.
QUESTIONS
• What factor causes terminal velocity to occur?
• If an object is at terminal velocity, is it speeding up,
slowing down, or falling at a constant speed?
• Describe and explain how forces change on a falling
object.
TERMINAL VELOCITY
Consider a skydiver:
1) At the start of his jump the air resistance
accelerates downwards.
zero
is _______
so he ________
2) As his speed increases his air resistance
will _______
increase
3) Eventually the air resistance will be big
balance the skydiver’s weight.
enough to _______
At this point the forces are balanced so
constant - this is
his speed becomes ________
called TERMINAL VELOCITY
How the forces change with time.
KEY
Gravity
(constant value & always
present…weight)
Air resistance
(friction)
Net force
(acceleration OR changing velocity)
TERMINAL VELOCITY
Consider a skydiver:
4) When he opens his parachute the
air resistance suddenly
increases
________,
causing him to start
slowing____.
down
_____
5)
Because he is slowing down his air
decrease
resistance will _______
until it
weight
balances his _________.
The
skydiver has now reached a new,
terminal velocity
lower ________
_______.
EXIT SLIP
• Must turn in lab!
• With questions answered correctly.