Chapter 4Linear 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  X “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 y x y o x o v y v x v oy Vox a y a x t t

25)For object moving only in y direction, Y = final position in y direction Y o = initial position in y direction V oy = initial velocity in y direction V fy = final velocity in y direction a y = -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 x o = initial position in x direction V ox = initial velocity in x direction V fx = final velocity in x direction a y = acceleration in x direction t = time elapsed

27) Kinematic Equations y = y o + v o t + ½ a t 2 V = v o + at x = x o + v o t + ½ a t 2 V = v o + 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