Physics Unit 1: Kinematics Flashcards Preview

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Flashcards in Physics Unit 1: Kinematics Deck (11):
1

Kinematics and Motion

Kinematics: study of motion (how objects move)

Motion: a change in the objects location as measured by a particular observer

2

Direction

Direction: the line an object moves along from a particular starting point
• Degrees on a compass
• Compass points (north, east, south, west)
• Up, down, left, right, forwards, backwards
• Expressed in brackets after distance Ex: 500 m [E] →object is 500 m to the east
-positive or negative

3

Scalar vs. Vector quantities

Scalar: a quantity that has only magnitude/size
• Distance
• Speed
• Mass
• Energy
• Temperature
• Potential/potential difference
• Density
• Time

Vector: a quantity that has both magnitude and direction. An arrow is placed above the symbol for a variable when it represents a vector quantity
• Displacement
• Velocity
• Acceleration
• Force
• Momentum
• Electric Field strength
• Magnetic field strength
• Gravitational field strength

4

Distances vs. displacement
-position

Distance (d) –scalar- the total length of the path travelled by an object in motion
Ex: Brick has been moved a distance of 5 m
• Differentiate between distance (magnitude quantity of displacement) and distance travelled (total length of a path travelled between two positions)

Displacement (delta d with arrow on top) –vector- the change in an object’s position. Displacement is the straight-line distance and direction from one point to another.
Ex: Brick has been displaced 5 m to the right

Position (d arrow on top) –vector- the distance and direction of an object from a particular reference point (ex: point 0 m)

• Displacement is simply the difference in the position of the two marks and is independent of the path taken in traveling between the two marks.
• The distance traveled, however, is the total length of the path taken between the two marks.


Ex: A person runs around circular track field that has a total of 400 m (distance). The overall displacement is 0 because the person ends up in the same position.

5

How to calculate displacement

Displacement = Final position (d arrow) – initial position (d arrow)

Changes position more than one:
• Displacement = displacement1 + displacement1
• If going opposite directions, make one direction – (ex: w – w instead of e)

6

Speed vs. velocity

Average Speed (Vav) – scalar- the total distance travelled divided by the total time elapsed
Vav= d/t
Ex: dog runs in a straight line for a distance of 43 m in 28 s. Average speed is 43m/28s = 1.5m/s

Average Velocity (V arrow on top av) –vector- the total displacement divided by the total time elapsed (needs direction and magnitude)

V arrow on top av = change displacement/change time

• Describes change in position over time
• Slope of a position-time graph gives the velocity of the object
• More rapidly an object’s position is changing, the greater is the magnitude of its velocity (depicted on position time graph as steeper slope)

7

Instantaneous velocity

Instantaneous Velocity: velocity at a specific instant in time (t = x). VInst = slope of the tangent to the position time graph at that instant in time

**speedometer in a car gives the instantaneous speed, whereas average speed would be for the entire journey

8

Average Acceleration

Average Acceleration: change in velocity divided by the total time elapsed (ms-2)

• Vector quantity
• An object is accelerating if it changes its velocity
• If an object is moving at a constant velocity, then no acceleration
• Direction depends on whether the object is speeding up or slowing down, and whether the object is moving in a + or – direction
o An acceleration of -2 m/s/s is an acceleration with a magnitude of 2 m/s/s that is directed in the negative direction.
*If an object is slowing down, then its acceleration is in the opposite direction of its motion.

9

Constant/uniform Motion
Non-uniform Motion

Uniform Motion: an object moves in a straight line at a constant speed (no changes in speed or direction)

Non-uniform motion (accelerated motion): an object changes speed or direction during its travel

Constant Acceleration: velocity is changing by a constant amount each time (constant rate)

10

Graphs:

Position-time
Velocity-time
Acceleration-time

Position-Time Graphs: position on x, time on y
• Slope = velocity
• Area means nothing

Velocity-Time Graphs: velocity on x, time on y
• Slope = acceleration
• Area = displacement

Acceleration-Time Graphs: acceleration on x, time on y
• Slope means nothing
• Area under curve = velocity

Approach to analyzing graphs:
1. Look at axis (what does y and x represent)
2. What does the slope represent
3. What does the area under the line represent
4. Identify parts of the line (i.e. increasing, decreasing, zero)

11

Velocity and Acceleration direction

The velocity is always in the SAME direction as the direction which the object MOVES.

Whenever an object SPEEDS up, its acceleration is in the SAME direction which the object moves.

Whenever an object SLOWS down, its acceleration is in the OPPOSITE direction which the object moves.