Representing MotionLinear motion motion in

a single dimension (in a line).A rate tells how

quickly something happens. Rate A quantity

divided by time

Motion is Relative

- Frame of Reference point of view of the

observer - If something is relative, it depends on the frame

of reference. - When we discuss the motion of something, we

describe its motion relative to something else. - Usually, when we discuss the speeds of things on

Earth, we mean the speed with respect to the

Earths surface.

Speed

- Speed is a measure of how fast something is

moving. - the rate at which distance is covered.
- Speed the distance covered per unit of time.
- SI unit m/s
- Ex 100 km/hr, 55 mph, 30 m/s
- Equation v d / t
- v speed (m/s)
- d distance (m)
- t time (s)

- Instantaneous speed
- the speed at any given instant
- Ex speedometer
- Average speed
- the total distance covered divided by the time

interval - Average speed does not indicate changes in the

speed that may take place during a trip. - BOTH instantaneous and average speeds indicate

the rate at which distance is covered.

Physics Problem Solving Strategy

- List your variables
- Givens
- Unknown variable
- If need be, convert variables to SI units
- Choose the equation that matches your variables
- Substitute variables in to the equation
- Solve

Check Your Understanding

- If a cheetah can maintain a constant speed of 25

m/s, it covers 25 meters every second. At this

rate, how far will it travel in 10 seconds? - d ?
- v 25 m/s
- t 10 s
- v d /t
- 25 m/s (d) / (10s)
- d (25 m/s)(10s)
- d 250m

Check Your Understanding

- In one minute?
- d ?
- v 25 m/s
- t 60s
- Convert minutes ? seconds
- v d / t
- 25 m/s (d) / (60s)
- d (25 m/s)(60s)
- d 1500m

Velocity

- When we say that a car travels 60km/hr, we are

indicating its speed. When we say that a car is

traveling 60km/hr to the north, we are indicating

its velocity. - Velocity the speed in a given direction
- SI unit m/s
- Ex 100 km/hr East, 55 mph North, 30 m/s

Southwest - Equation v d / t
- Speed is a description of how fast an object

moves velocity is how fast it moves AND in what

direction .

Check Your Understanding

- The speedometer of a car moving northward reads

100 km/h. It passes another car that travels

southward at 100 km/h. Do both have the same

speed? Do they have the same velocity? - Both cars have the same speed, but they have

opposite velocities because they are moving in

opposite directions.

- Constant Velocity
- Constant velocity requires both constant speed

and constant direction. - Motion at constant velocity is in a straight line

at constant speed. - Changing Velocity
- Constant speed and constant velocity are not the

same thing. - A body may move with constant speed around a

curved path, but it does not move with constant

velocity because the direction changes at every

instant.

Vector and Scalar Quantities

- Scalar a quantity that requires magnitude only
- Number and units ONLY
- Ex Speed, mass, time
- Vector a quantity that requires both magnitude

AND direction - Number, units, AND direction
- Ex Velocity, acceleration, force

Check Your Understanding

- Is height a scalar or vector quantity?
- Scalar. Height only includes magnitude (how big

the number is) only and NOT direction. You are

58 tall, not 58 to the east.

Adding Vectors

- An arrow is used to represent the magnitude

direction of a vector quantity. - The length of the arrow indicates the magnitude

of the vector quantity. - The direction of the arrow represents the

direction of the vector quantity. - When more than one vector combines together, both

the magnitude AND the direction matter. - The sum of 2 or more vectors is called the

resultant.

- Arrows that point in the same direction are added

together to find the resultant. - 4 m/s N 3 m/s N 7 m/s
- Arrows that point in opposite directions are

subtracted to find the resultant. - 4 m/s N 3 m/s S 1 m/s
- When arrows are at right angles to each other,

the diagonal of a rectangle will determine the

resultant. - Use the Pythagorean theorem a2 b2 c2
- (4m/s N)2 (3 m/s E)2 16 9 25 (5 m/s NE)2

Check Your Understanding

- A boy is riding his bike down the street at a

speed of 10 m/s. A gust of wind came out of

nowhere headed towards the boy. If the wind is

traveling 3 m/s, what will the boys new speed

be? - Since the boy and the wind are moving in opposite

directions, we need to subtract their speeds to

find the resultant. - 10 m/s 3 m/s 7 m/s

Position - Time graphs

- Position-Time graphs show the distance covered

over an elapsed time - Aka Distance-Time graphs and Displacement-Time

graphs - Time is always the independent variable

- Position (distance) is always the dependent

variable - The slope of a Position-Time graph is equal to

velocity - Slope rise/run
- Slope position / time
- Velocity position / time
- The steeper the slope, the faster the velocity
- A positive slope is forward motion
- A negative slope is moving backwards
- A zero slope is NOT moving at all

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Check Your Understanding

- Which person is moving faster, the red or blue

jogger? - The red jogger. The red joggers line has a

steeper slope and therefore a faster speed.

Check Your Understanding

- Are both joggers moving forwards or backwards?
- Forwards. The slope is positive, meaning that

the distance increases over time.

Check Your Understanding

- At what time does Person B pass Person A?
- At 45 seconds. The lines intersect at this time

and both runners are at the same position at the

same time.