physics on the road - lesson 8
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Falling downFalling downPhysics On the Road
Lesson 8
LI…Describe free fall.Use kinematic equations to
make predictionsExplain parabolic projectile
motion.
Free fall
Gravity is uniform acceleration
Galileo first proposed the idea that all objects fall with uniform acceleration.
He proved it by rolling balls down slopes
It is an idea with far reaching implicationsGravity accelerates all
objects on Earth at a rate of 9.8 ms-2
Air resistance
Why doesn’t it look like all objects fall at the same rate.
Gravity is not the only force acting.
Air resistance acts against motion.
The air resistance depends upon size, shape but mostly speed.
Falling down Describe a parachute jump using a
velocity time graph.
time
velo
city
Still falling down Explaining a parachute jump Use the idea of forces
time
velo
city
w
w
w
f
w
f
w
f
Ignore air resistance - constant acceleration
∆v
∆t
∆t
t=0
2∆v
If you ignore air resistance falling objects gain speed at the same rate.They accelerate at Earth at a rate of 9.8 ms-2.
Q1. How far will a coin fall in 5 seconds?
0 ms-1
9.8 ms-1
19.6 ms-1
Sideways makes no difference
∆v
∆t
∆t
t=0
2∆v
0 ms-1
9.8 ms-1
19.6 ms-1
∆v
2∆v
9.8 ms-1
19.6 ms-1
Changing velocity in a parabolic path -vectors
v
∆v
v
v v
v
v
Due to gravity
v∆v
newv
v
∆vnewv
Demonstrate Your Understanding
Explain why this trick is not as dangerous as it looks.
EXTENDED ANSWER TASK
Use diagramsUse principlesUse vectorsUse calculations