Physics Chapter 3 and 5 Velocity, Acceleration, and Falling Bodies
Reference Point – the point that all objects are measured from
What is similar about these two clips?
What is different about these two clips?
They are similar because they both traveled the same distance (10 yards)
The are different because one traveled forward and the other traveled backwards.
Scalars vs. Vectors
The distance is the separation between objects. It does not have a direction and is called a scalar
The position or displacement is the separation between the object and the reference point. It does have a direction and is called a vector
Displacement – change in position;
What is the displacement of the runner in the clip?
What is the distance traveled?
Speed and Velocity
Speed is simply saying that Ed here is going 80 mph.
Speed is a scalar.
Velocity is saying that Ed is going 80 mph in a easterly direction.
Velocity is a vector.
Average Velocity – the total displacement over the time interval
v = d f – d i / t f – t i
Constant velocity – the average velocity is the same for all time intervals – Zero acceleration
Is a merry go round experiencing constant speed or constant velocity?
The answer is …
Constant speed because its direction is constantly changing.
Instantaneous position – the location of an object at a single instant
The slope on a position-time graph gives you constant velocity
Curves on a P-T Graph Constant positive velocity (going forward) Constant negative velocity (going backward) Zero Velocity (not moving) Accelerating P o s i t i o n Time
Position-Time Graph 15 10 5 Meters (m) 2 4 6 8 10 12 14 Time (s)
Displacement after 4 seconds
Displacement after 14 seconds
Distance traveled after 14 seconds
Velocity from 0-4 sec
Velocity from 4-10 sec
Velocity from 10-14 sec
Acceleration from 0-4 sec
0 m/s 2
Instantaneous velocity – velocity of an object at a single instant
Ex: Your speedometer
V-T graphs: the slope of these graphs gives you acceleration
Also, the area under the curve of a velocity-time graph gives you the displacement
Acceleration is the change in velocity.
A = V f – V i / t
Curves on a V-T Graph Constant positive acceleration (speeding up in positive direction) Constant negative acceleration (slowing down in positive direction Zero acceleration (constant positive velocity) Constant positive acceleration (Slowing down in the negative direction) Constant negative acceleration (speeding up in the negative direction) Zero acceleration (constant negative velocity) Velocity Time
15 10 5 Velocity (m/s) 1 2 3 4 5 6 7 Time (s) 8 9 Velocity-Time Graph
Velocity after 2 sec
Velocity after 9 sec
Acceleration from 0-2 s
Acceleration from 2-4s
Acceleration from 4-6 s
Acceleration form 6-9s
Displacement from 0-2 s
Displacement from 0-9 s
5 m/s 2
0 m/s 2
2.5 m/s 2
-5 m/s 2
Always remember that motion is relative.
The earth is usually our reference point to determine our speed.
We are all traveling the same speed relative to the sun.
Relative Velocity 45 MPH 60 MPH
What is the velocity of the blue car relative to the green car?
What is the velocity of the green car relative to the blue car?
Relative Velocity 55 MPH 40 MPH
What is the velocity of the blue car relative to the red car as they head towards one another?
What is the velocity of the blue car relative to the red car as they head away from one another?
v= v 0 +at
d= 0.5(v+v 0 )t
d = V 0 t + 0.5at 2
v 2 = v 0 2 + 2ad
V = final velocity
V 0 = initial velocity
t = time
a= g = -9.8m/s 2
If something is dropped v 0 = 0
At its highest point, an object’s velocity is 0
If an object is falling its displacement is negative.