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Physical Science

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Physical Science

Chapter 11 – Part 1

Non-accelerated Motion

Chapter 11.1-11.2

- A system of objects that are not moving with respect to one another
- A reference point or system
- BASICALLY …. Something unchanging to measure things from
- Good frames of reference for measuring the motion of a car…
- The Earth, the road, buildings, trees

- Bad frames of reference for measuring the motion of a car….
- Clouds, other cars on the road, bikers, flying birds

- Movement in relation to a frame of reference
- All Motion is Relative
- This means… all motion is based on someone’s or something’s perspective

- Examples
- School busses
- Cars on highway
- LabQuest

Or a more recent example

- Length of a path between two points
- When an object moves in a straight line, the distance is the length of a line connecting the starting point and the ending point
- SI Unit – meters
- Other options- km, mi, cm

- Distance with a direction
- Distance – 5 kilometers
- Displacement – 5 Kilometers North

- How much an object is displaced
- When objects travel in a straight line the magnitude (amount) of the displacement is equal to the distance travelled
- When an object does not travel in a straight line, distance and displacement will be different

- Vector Quantities
- Have magnitude and direction

- Scalar Quantities
- Only have magnitude

- Vector quantities can be represented with arrows of a scaled length
- Length shows magnitude
- Arrow shows direction

3 km

3 km

3 km + 3 km = 6 km

4 km

7 km

4 km + 7 km = 11 km

8 km

- 5 km

8 km - 5 km = 3 km

- Resultant Vector (red) – vector sum of 2 or more vectors

3 km

5 km

2 km

Finding Distance Using Scalar Addition 1+1+2+3 = 7 km

Finding Displacement using Vector Addition = 5 km NE

1 km

1 km

- These two vectors have the same ________________ and opposite ________________.

- These two vectors have different ________________ but the same ________________.

- These two vectors have the same ________________ AND the same ________________.

- Average Speed is equal to distance divided by time
- How fast or slow something is going
- A rate of motion

- Speed at a given moment of time
- What the speedometer on a car reads

- When speed is not changing
- Instantaneous speed is equal to average speed at all times
- NOT Speeding up or slowing down
- Only ways to change speed is to speed up or slow down

- Speed AND direction that an object is moving
- Vector Quantity
- + or – sign indicates which direction the velocity is
- + means North, Up, East, or to the Right
- - means South, Down, West, or to the left

- Sometimes multiple velocities can affect an objects motion
- Sailboat, airplanes
- These velocities combine with Vector Addition

- Speed – tells how fast something is moving
- Ex. 100 km/hr

- Velocity – tells how fast something is moving and its direction
- Ex. 35 mph North

- Can an object move with constant speed but have a changing velocity?
- Can an object move with constant velocity but have a changing speed?

- Acceleration – The rate at which velocity changes
- Can be described as ….
- Changes in Speed
- Changes in Direction
- OR change in both Speed and Direction

- Vector Quantity
- Units are meters per second per second or m/s2

Can an object moving with constant speed be accelerating?

- Divide the change in velocity by total time

- A car starts from rest and increases its speed to 25 m/s over the course of 10 seconds. What is the car’s acceleration?

- Motion can also be depicted very well using graphs
- Two types of graphs
- Displacement vs. time (D-t) graphs
- Velocity vs. time (V-t) graphs

Straight,upward line on a V-t graph means constant acceleration

Straight,upward line on D-t graph means constant velocity

Displacement (m)

- Displacement increases at regular intervals, so constant velocity
- Graph below Increases displacement by 5 meters every sec.

- To find vel. on a disp.- time graph, find Slope

- Tells the rate of increase of the y-value as you move across the x values for any graph
- Slope = rise / run
- In other words… how much the graph goes up divided by how much the graph goes across

- Slope tells us properties of the motion being depicted
- On a displacement time graph slope = velocity
- On a velocity-time graph slope = acceleration

Rise/run=slope= 25/5 =

5 m/s

Rise = 25

If you took slope of smaller sections of the graph you would get the same answer since ‘v’ is constant

Run = 5

- v v. t graphs may look the same as some D v. t graphs, but the motion they describe can be very different because they deal with velocity, not distance.
- **The slope, of a Velocity v. Time graph indicates Acceleration**.

What is v for 0-1 sec.??

What is v for 0-2 sec.??

What is v for 3-5 sec.??

What is v for 0-5 sec. ??

- Parabola….. If + acc, line keeps getting steeper and steeper

d

t

- Avg. velocity from 0-1 sec. ? 4 m/s
- Avg. vel. From 3-4 sec? 16.5
- Acc. From 2-3 sec? 7 m/s2

Velocity (m/s)

- Speed-time graph
- Slope = rise/run …
- Rise =
- 16

- Run =
- 4

- Rise/run =
- 4 m/s = acceleration

- Position –time Graph
- Slope = rise/run …
- Rise =
- 50

- Run =
- 5

- Rise/run =
- 10 m/s = speed

- As objects fall toward the Earth they are accelerating at a rate of 9.8 m/s2 downward
- We can usually round 9.8 m/s2 to 10 m/s2
- Objects in free fall will gain 10 m/s of speed for every 1 second it is falling

- Object is in free-fall any time it is ONLY under the influence of gravity
- Including when something is thrown upwards

- All objects (regardless of mass) fall at the same rate on Earth, when air resistance is ignored

Ball thrown upward with initial velocity of +30 m/s