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

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## Kinematics and Motion

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Kinematics: study of motion (how objects move)

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

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## Direction

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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

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## Scalar vs. Vector quantities

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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

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##
Distances vs. displacement

-position

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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.

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## How to calculate displacement

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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)

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## Speed vs. velocity

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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)

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## Instantaneous velocity

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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

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## Average Acceleration

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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.

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##
Constant/uniform Motion

Non-uniform Motion

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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)

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##
Graphs:

Position-time

Velocity-time

Acceleration-time

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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)

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