Chapter 4 Linear motion 1 You can describe
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 changes or 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 speed time 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/sec 2
24) 6 kinematic variables in y and x yo xo vy vx voy Vox ay ax t t
25)For object moving only in y direction, Y = final position in y direction Yo = initial position in y direction Voy = initial velocity in y direction Vfy = final velocity in y direction ay = -g t = 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 direction xo = initial position in x direction Vox = initial velocity in x direction Vfx = final velocity in x direction ay = acceleration in x direction t = time elapsed
27) Kinematic Equations y = y o + v ot + ½ a t 2 V = vo + at x = x o + v ot + ½ a t 2 V = vo + at
28) For An object dropped from height h in free fall, equations simplify y = h - ½ g t 2 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
- Slides: 32
