Transcript Motion Powerpoint, Part A File

Dynamics is the study of things that move,
and why they move.
Basic equation
distance
speed 
time
d
m
1
v
units
 ms
t
s
km 1000m
1
1
1


ms
h
3600s 3.6
• The motorcycle was traveling at 250 km/h.
• Convert this to ms-1
• “See- think- react” usually takes 1 second.
• How far does the rider travel before
braking?
• the bike rider was found INSIDE the car.
• The Volkswagen actually flipped over from
the force of impact and landed 3 m from
where the collision took place.
Acceleration equation
change in velocity
acceleration 
change in time
m / s ms
units 

s
s
1
 ms
2
Kinematic Equations
v f  vi  at
1 2
d  vi t  at
2
v  v  2ad
2
f
2
i
• A cliff on the Milford Track is called
“10 second cliff”
• Why?
• How high is it?
Displacement/time Graphs
(not assessed)
d
stationary
t
d
Moving forward
constant velocity
t
• Displacement Time Graph
STOP
d
constant
Velocity (L)
STOP
t
stopped
constant
Velocity (R)
constant
constant
Velocity (L)
Velocity (R)
For a displacement/time graph
• Positive slope means moving to the right
Negative slope means moving to the left
Δd
d
Δt
Gradient = Rise = Δ d = velocity
Run
Δt
t
Constant gradient
d
Constant velocity
t
Increasing gradient
d
acceleration
t
Decreasing gradient
d
decceleration
t
d
acceleration
t
d
decceleration
t
Velocity/time Graphs
(not assessed)
Increasing V
constant V
decreasing V
decreasing V
Increasing V
V
t
Positive velocity : Moving to the right
accelerating
deccelerating
constant velocity
v
t
Negative velocity : Moving to the left
accelerating
deccelerating
Positive area,
moving to the right
Negative area,
moving to the left
Δv
v
Δt
Gradient = Rise = Δ v = acceleration
Run
Δt
t
Scalars and Vectors
Scalars
Vectors
have only size
have size and direction
Distance
Speed
Displacement
Velocity
Acceleration
Force
m
ms-1
ms-2
N
Vectors
Adding Vectors.
When is 3 + 3 not equal to 6?
Courtney rides 3 km north then 3 km south.
What is her displacement?
In this case 3 + 3 = 0 if you take into account
direction.
Sarah rides 3 km north then 3 km east.
What is her displacement?
Displacement is
3 3
2
Direction is
0450
2
• So you can see that to ADD vectors, you
put them tail to head.
• The total is from tail to head
B
A
To find A + B
A+B
• The order doesn’t matter
B
A+B
A
To find A + B
Adding Forces
What size is the total (net) force?
300 N
300 N
What size is the total (net) force?
600 N
300 N
Find the Net Force
300 000N
900
300 000N
TAIL to HEAD
900
TAIL to HEAD
A Skier on the Slope
why does her acceleration depend on
the angle of the slope?
consider the forces on her
consider the forces on her
consider the forces on her
θ
θ
changing the angle
Adding Velocities
• Jess is walking at 3.0 ms-1 in the bus.
• The bus is moving at 4.0 ms-1
• What is her velocity if…..
Adding Velocities
• Jess is walking at 3.0 ms-1 in the bus.
• The bus is moving at 4.0 ms-1
• What is her velocity if…..
Adding Velocities
• Jess is walking at 3.0 ms-1 in the bus.
• The bus is moving at 4.0 ms-1
• What is her velocity if…..
River and Boat
• A plane is pointing north with an airspeed
of 400 kmh-1.
• The wind is from the west at 300 kmh-1.
• What is the plane’s ground velocity?
Plane in still air
Plane pushed by wind.
Wind/ground
Plane/air
plane/ground
θ
Speed =
300  400
300
tan  
400
2
2
What direction must the plane point
so it flies north?
Plane in still air
Plane pushed by wind.
Wind/ground
plane/ground
Plane/air
Wind/ground
What is the ground speed?
plane/ground 4002  3002  ground speed 2
What direction does
the pilot point?
Plane/air
φ
300
sin  
400
Change in Velocity
• The change in anything is what it is
minus what it was.
• Confused????????
• What is the change in your height in the
last 5 years?
• Height change= height now – height then
h  h f  hi
• You had $5 yesterday now you have $10
• What is the change in your wealth?
• You had $10 yesterday now you have $5
• What is the change?
• You had $5 yesterday now you owe $10
• What is the change?
Vi = 5 ms-1
Vf = 0 ms-1
What is the ball’s change in velocity?
5 ms-1
3 ms-1
What is the ball’s
change in velocity?
v  v f  vi
 v f  (vi )
Δv
vi
vf
-vi
vf
What direction is the
force of the floor on
the ball?
Velocity
change
Velocity change and
force are in the same
direction
force
• What is the velocity change if the ball hits
on an angle?
vi
v  v f  vi
vf
 v f  (vi )
Δv
-vi
vf
-vi
vf
Components
• We have seen that you add vectors tail to
head.
• You can also separate a vector into two
parts at right angles.
• The parts are called components.
OR
The force from the rope can be split into two
components
The horizontal component pulls her forward
The vertical component tries to lift her.