Lecture 3, Linear Kinematics - Describing Linear Movements

Question 1

What does it mean to move?
How do we quantify movement?

Answer 1

• a change in position
• where we are in space and how long did it take

Question 2

Linear Change & Angular

Answer 2

linear change - a change in position (start in one place and physically relocate to another place)
- translation, change position and move in the same direction

angular - a change in orientation (just rotating for example - anchored to the same spot)
- rotation, changing orientation, spin around the same fixed axis

Question 3

General Motion

Answer 3

a combination of linear and angular motion
- we analyze one at a time and break movements down into its individual components and than make comment about both as a whole as it can get complicated when looking at both at the same time
- we you are walking you are changing position but when you need to turn a corner around a sidewalk you are also change orientation - the combination of linear and angular motion

Question 4

Linear Motion

Answer 4

• linear motion occurs when all points on a body or object move at the same distance, in the same direction and at the same time
• linear motion is also referred to as translation - changing position (start in one position and body moves yo completely new position)

Question 5

What are the two types of linear or translatory action?

Answer 5

rectilinear motion: movement along a straight line
example: elevator, bowling, running the 100m dash (the intention is to remain straight but there can be little deviations)

curvilinear motion: movement along a curved line
example: flight path of a ball, riding around a corner
- does not have to be a continuous curves - can wean back and forth

Question 6

Linear Kinematics

Answer 6

• linear motion occurs when all points on a body or object move the same distance, in the same direction and at the same time
• kinematics is the description of movements, without getting into what causes those movements
• so, linear kinematics in concerned with the description of linear motion
• questions about speed, distance and direction are all inquires about the linear kinematics of an object

my notes:
- your are intact object (rigid-body mechanics) that moves along the same path (start in one and end up in different)
- there is no discussion of forces in kinematics (do not associate force with kinematics)
- how far you moved, how fast you moved, are you in static (constant) or dynamic state of motion

Question 7

Position

Answer 7

• the first kinematic characteristic we might describe about an object is its position
• our definition of motion (the process of change) refers to position
• mechanically, position is defined as location in space
  ◦ example: identifying where a
  system is at the start or end of
  an action
• position could be described in one, two or three dimensions
  ◦ up/down, left/right and
  forward/back
• to describe position, we need to identify a starting point for movement so we can then explore the direction of travel

Question 8

Spatial Reference Systems

Answer 8

• it is often useful to have a fixed system of reference to standardize the measurements taken
• the system most commonly used is a Cartesian coordinate system
• movements that are primarily in a single direction (or planar) can be analyzed using two dimensions; points of interest are measured in the x or horizontal direction and in y or vertical direction
• the origin of the movement or the starting point can be measured with respect to the two axes and described as the number of steps away from each line
• these steps can be measured as positive or negative depending upon the direction of travel

Question 9

Distance Traveled and Displacement

Answer 9

describing motion: locating the position of an object in space
distance (l): the total length of travel - scalar quantity
displacement: a change in position - vector quantity
my notes:
- scalar is just a number, big or small, magnitude (no direction) - like how much mass you are made of (scale)
- when describing movement you can look at where you are in space, where you started and the path you took
- displacement is a vector quantity that takes into account where you start and finish and direction (left, up, down, right - a positive or negative sign will be present)

Question 10

Temporal Patterns of Movement

Answer 10

speed and velocity measure how fast or slow a system moves
speed (s): change in distance / change in time - scalar quantity
s = (l2 - l1) / (t2 - t1)

velocity (v): change in displacement / change in time - vector quantity
v = (d2 - d1) / (t2 - t1)

my notes:
- speed is a scalar concept - takes into account distance with change in time (how far did you travel and the time period in which you travelled) - no direction with signs
- velocity is still how fast or slow but it is a different quantity as there is also going to be a sign implying a direction
- both give a quality of performance in regards to timing

Question 11

Acceleration

Answer 11

dynamic motion is characterized by a change in velocity
forces produce a change in velocity
- acceleration = change in velocity / change in time
- a = (v2 – v1) / (t2 – t1)
vector quantity
base unit is in meters / second2 (m/s2)

my notes:
- if your velocity is changing then you are accelerating
- in order to produce acceleration you need force (no force present means no acceleration)
- acceleration is also a vector quantity (magnitude how big or small and direction)
- acceleration looks at velocity with respect to change in time to it is squared
- change in speed is not acceleration only change in velocity

Question 12

Movement Often Change Over Time

Answer 12

acceleration can be positive, negative, or zero
* if v2 > v1, a is positive
◦ the system is accelerating
(speeding up, a dynamic state)
* if v2 < v1, a is negative
◦ the system is decelerating
(slowing down, a dynamic
state)
* if v2 = v1, a is zero
◦ no change in the system (static
state)
so, the sign can indicate the state of the system

my notes:
- the sign in acceleration can tell you if you are going slower or faster
- speeding up means the number is getting bigger (dynamic state = velocity is changing)
- static state (go be motionless or moving in a constant manner)