Transcript Freefall

1-D Projectile Motion
First Some Definitions
• Projectile – An object that only has the
force of gravity acting on it.
• Trajectory- path a projectile travels
through space
• Apex-highest point reached along a trajectory
Free Body Diagram
Hint: Remember the definition of a projectile
Free Body Diagram
Hint: Remember the definition of a projectile
Does the ball travel the
same distance every
second?
Does the ball travel the
same distance every
second?
No. The ball travels
more distance per
second as it falls.
Is the ball’s velocity
constant as it falls?
Is the ball’s velocity
constant as it falls?
No, It decreases by 10 m/s
every second
So…...
is the acceleration
constant?
Yeah …
a = -10 m/s2 the whole time
We can find the velocity at any time
Velocity of Free Falling Projectile
a is the acceleration due to
gravity (g)
Now to find the distance…
The distance increases as the square of the
time
Problems
• A 3-kg watermelon is dropped off the Sundial
restaurant in downtown Atlanta. It takes 3
seconds to hit the ground.
1. What is the velocity of the watermelon on
impact?
2. How far had the watermelon fallen by the 2nd
second?
3. How tall is the Sundial restaurant?
4. What is the weight of the watermelon at the top
of the restaurant?
1. v= gt; v = (10)(3) = 30 m/s
2. d = 1/2gt2 ; d= ½ (10)(2)2 = ½(10)(4) = 20 m
3. d = 1/2gt2 ; use 3s since that’s how long it
took to fall from the top; d= ½ (10)(3)2 =
½(10)(9) = 45 m
4. Fw = mg = (3kg)(10) = 30 N
Conditions/assumptions for freefall
projectile
• Gravity is the force that causes the acceleration
(the change in velocity)
• Assume no air resistance during freefall, so
acceleration due to gravity is a constant 10 m/s2
• Assume object start from rest (initial velocity will
be zero)
• Velocity can be calculated at any instant (v=gt)
• Distance traveled can be calculated at any
instant
(d = ½ gt2)
Questions
• When an object is in freefall:
• Does its velocity change by regular amounts each
second that it’s falling? If yes, why; if no, why
not?
• Yes, changes by ten for every second the object
falls
• Is the distance it falls per second the same
amount each second? Explain why.
• No, as it falls it gets faster so for every second it
falls it covers more distance per second