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Physical Science. Chapter 11 – Part 1 Non-accelerated Motion Chapter 11.1-11.2. Frame of Reference. 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

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Physical science

Physical Science

Chapter 11 – Part 1

Non-accelerated Motion

Chapter 11.1-11.2


Frame of reference

Frame of Reference

  • 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


Relative motion

Relative Motion

  • 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


Relative motion1

Relative Motion

Or a more recent example


Measuring distance

Measuring Distance

  • 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


Displacement

Displacement

  • 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


Vectors

Vectors

  • 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


Vectors scalars

Vectors & Scalars


Displacement in a straight line

Displacement in a straight line

4 km

7 km

4 km + 7 km = 11 km

8 km

  • 5 km

8 km - 5 km = 3 km


Displacement that isn t on a straight path

Displacement that isn’t on a straight Path

  • 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


Physical science

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


Physical science

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


Physical science

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


Average speed

average Speed

  • Average Speed is equal to distance divided by time

  • How fast or slow something is going

  • A rate of motion


Instantaneous speed

Instantaneous Speed

  • Speed at a given moment of time

  • What the speedometer on a car reads


Constant speed

Constant Speed

  • 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


Velocity

Velocity

  • 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 vs velocity

Speed vs. Velocity

  • 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

acceleration

  • 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


Physical science

Can an object moving with constant speed be accelerating?


Devices in cars that lead to acceleration

Devices in Cars that lead to acceleration


Calculating acceleration

Calculating Acceleration

  • Divide the change in velocity by total time


Example

Example

  • 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?


Graphs of motion

Graphs of motion

  • 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)


D t graph of constant v

D-t graph of constant ‘v’

  • 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


Slope

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


Velocity time graphs

Velocity- Time graphs

  • 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**.


Distance time graph of changing velocity

Distance-time graph of changing velocity

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. ??


Distance time graph of constant acceleration

Distance-time graph of constant acceleration

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

d

t


Physical science

  • 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 vs time graph of constant acceleration

Velocity vs. Time graph of constant acceleration

Velocity (m/s)


Physical science

  • 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


Free fall acceleration

Free Fall Acceleration

  • 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


Free fall acceleration1

Free Fall Acceleration

  • 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


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