Chapter 4Linear motion. 1) You can describe the motion of an object by its position, speed,...
Transcript of Chapter 4Linear motion. 1) You can describe the motion of an object by its position, speed,...
Chapter 4 Linear motion
1) You can describe the motion of an object by its position, speed,
direction and acceleration
2) Distance is a scalar.
Distance is “how much ground is covered” during motion.
3) Displacement is a vector
Displacement is DX “final position – initial position”
4) Motion is relative.An object is moving if its position relative to a fixed point is changing.
5) 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.
6) Unless stated otherwise, we measure speed relative to the Earth.
7) Speed is how fast an object is moving. Speed is a scalar quantity.
8) From motion experiments, Galileo defined Speed = distance/time
Before Galileo, motion was simply described as “fast” or “slow”
9) Instantaneous speed is the speed at any instant.
10) A speedometer shows instantaneous speed.
11) Average speed = total distance time interval
12) Velocity = speed in a given direction. Velocity is a vector quantity.
13) Constant velocity = means same speed
in same straight-line direction.
14) Changing velocity : if either the speed changes
or the direction changesor both change
15) Acceleration is the rate of change of velocity
acceleration is a vector.
16) acceleration = change of velocity time interval
17) Deceleration = decrease in acceleration
18)Acceleration is due to change in direction of moving object
19) Accelaration for object in a straight line
= change in speedtime interval
Free fall
20) projectile: an object that moves only under the influence of gravity.
21) Free fall = object falling under influence of gravity.
22) When we talk about free fall, we ignore air resistance.
23) Acceleration of object in free fall is about g= 10 meters/sec2
24) 6 kinematic variables in y and x
y xyo xo
vy vx
voy Vox
ay ax
t t
25)For object moving only in y direction,
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
26) What is meant by “-g”?
The object is accelerating in the negative direction
27) For object moving only in x direction
x = final position in x directionxo = initial position in x directionVox = initial velocity in x directionVfx = final velocity in x directionay = acceleration in x directiont = time elapsed
27) Kinematic Equations y = yo + vot + ½ a t2
V = vo + at
x = xo + vot + ½ a t2
V = vo + at
28) For An object dropped from height h in free fall, equations simplify
y = h - ½ g t2
V = -gt
26) Rising objects: an object thrown straight up will slow
down, stop and fall back down
27) At the highest point, the vertical velocity is zero.
28) Projectile motions