Chapter 4 Linear motion
1) Linear means in a straight line
2) Describe the motion of an object by its position,
speed, direction
and acceleration
3) Distance is a scalar.
Distance is “how much ground is covered” during motion.
4) Displacement is a vector
Displacement is DX “final position – initial position”
5) Example: distance is the path length
from o to c
Example: distance is the path length
from a to c
But displacement is the vector from a to c = final position – initial position
6) Motion is relative.An object is moving if its position relative to a fixed point is changing.
7) Example: A crate on a train traveling at 20 m/sec.
The crate is at rest wrt the train.
But the crate is moving 20 m/sec relative to the ground.
8) Unless stated otherwise, we measure speed relative to the Earth.
7) Speed is how fast an object is moving. Speed is a scalar quantity.
10) From motion experiments, Galileo defined Speed = distance/time
11) Before Galileo, motion was simply described as “fast” or “slow”
12) Instantaneous speed is the speed at any instant.
13) A speedometer shows instantaneous speed.
11) Average speed = total distance time interval
15) Velocity = speed in a given direction.
Velocity is a vector quantity.
16) Constant velocity = means same speed
in same straight-line direction.
17) Changing velocity : if either the speed changes
or the direction changesor both change
18) Acceleration is the rate of change of velocity
acceleration is a vector.
19) acceleration = change of velocity time interval
20) Deceleration = decrease in acceleration
21) Accelaration for object traveling in a straight line
= change in speedtime interval
Free fall
22) projectile: an object that moves only under the influence of gravity.
23) Free fall = object falling under influence of gravity.
24) Trajectory = path of a projectile
25) When we talk about free fall, we ignore air resistance.
26) Acceleration of object in free fall is about g= 10 meters/sec2
27) Kinematics is the study of motionGalileo discovered these relationships.
28) There are 6 kinematics variables and 2 kinematics equations
29)Kinematics variables for free falling object,
Y = final position in y directionYo = initial position in y directionVoy = initial velocity in y directionVfy = final velocity in y direction
ay = -gt = time elapsed
30) What is meant by “-g”?
The object is accelerating in the negative direction
31) Kinematic Equations y = yo + vot + ½ a t2
V = vo + at
x = xo + vot + ½ a t2
V = vo + at
32) For freefall, equations simplify to
y = - ½ g t2
V = - gt
33) Rising objects: an object thrown straight up will slow
down, stop and fall back down
34) At the highest point, the vertical velocity is zero.
28) Projectile motions
1-D 1-D 2-D