MotionMotion

Motion - Beware of moving Motion - Beware of moving objectsobjects

In the study of motions objects will In the study of motions objects will be moving.be moving.

TermsTerms– A) Distance vs. DisplacementA) Distance vs. Displacement– B) Speed vs. VelocityB) Speed vs. Velocity– C) AccelerationC) Acceleration– D) Acceleration due to GravityD) Acceleration due to Gravity

MeasurementsMeasurements

All measurements must include a All measurements must include a unit!unit!

Without a unit the answer is Without a unit the answer is incomplete.incomplete.

For example: For example:

A) Distance vs. DisplacementA) Distance vs. Displacement

Distance - measures the total Distance - measures the total amount of area covered.amount of area covered.

If we start at point A and end at point If we start at point A and end at point A the distance traveled is found:A the distance traveled is found:

4m

8m

Add up all the legs of the journey:

4m + 8m + 4m + 8m = 24m

A

A) Distance vs. DisplacementA) Distance vs. Displacement

Displacement is another word for Displacement is another word for position. position.

For position the only important For position the only important value is how far apart are the value is how far apart are the starting and ending point!starting and ending point!

4m

8mA

To calculate displacement:

1. Observe the starting and ending points.

2. Calculate the distance between the two.

A) Distance vs. DisplacementA) Distance vs. Displacement

In this example the start and end In this example the start and end point are the same. point are the same.

The total displacement is then 0m. The total displacement is then 0m.

4m

8mA

A) Distance vs. DisplacementA) Distance vs. Displacement

Calculate the Distance and Calculate the Distance and Displacement of the following:Displacement of the following:

500mStart End

Start/End

B) Speed vs. VelocityB) Speed vs. VelocitySpeed is a measure of how Speed is a measure of how quickly distance is covered.quickly distance is covered.

Words “How quick” = time.Words “How quick” = time.

Speed = Distance/TimeSpeed = Distance/Time– Measured in m/sMeasured in m/s– Scalar MeasureScalar Measure– Positive speed --> going fasterPositive speed --> going faster– Negative speed --> slowing down Negative speed --> slowing down

B) Speed vs. VelocityB) Speed vs. Velocity

Velocity measures how quickly the Velocity measures how quickly the position of an object changes.position of an object changes.– Velocity = Displacement/TimeVelocity = Displacement/Time– Velocity is a vectorVelocity is a vector– Unit is m/sUnit is m/s

v = s/t

B) Speed vs. VelocityB) Speed vs. Velocity

A car travels A car travels 400m in 20sec. 400m in 20sec. What is its speed?What is its speed?

– v = s/tv = s/t– v = 400m/20secv = 400m/20sec– v = 20m/sv = 20m/s

A student has a speed of 10m/s for 6 seconds. How far does the student travel?

v = s/t10m/s = s/6secs = (10m/s)(6sec)s = 60m

C) AccelerationC) Acceleration

Acceleration measures the rate at Acceleration measures the rate at which an object which an object changeschanges velocity. velocity.

To calculate acceleration 2 To calculate acceleration 2 measures of velocity must be measures of velocity must be known: starting and ending. known: starting and ending.

The period of time must also be The period of time must also be measured.measured.

C)AccelerationC)AccelerationAn object accelerates (changes its An object accelerates (changes its velocity) in a couple of ways.velocity) in a couple of ways.– Increases velocityIncreases velocity– Decreases velocityDecreases velocity– Changes directionChanges direction

When an object DOES NOT change When an object DOES NOT change velocity/direction it is not velocity/direction it is not accelerating.accelerating.

C) AccelerationC) Acceleration

C) AccelerationC) AccelerationAcceleration is abbreviated with the Acceleration is abbreviated with the symbol a.symbol a.It is a vector measurement.It is a vector measurement.Compares changes in velocity over a Compares changes in velocity over a period of time. period of time. The unit is m/sThe unit is m/s22

a = (vf-vi)/∆t

C) AccelerationC) AccelerationThe bowling ball in my hands is at rest. When I throw it at The bowling ball in my hands is at rest. When I throw it at you it hits your head with a final velocity of 12m/s. The ball you it hits your head with a final velocity of 12m/s. The ball takes 3 seconds to hit you. What is the ball’s acceleration?takes 3 seconds to hit you. What is the ball’s acceleration?

a = (vf-vi)/∆tvi = 0m/svf = 12m/st = 3st = 3s

a = (12m/s-0m/s)/3sa = (12m/s)/3sa = (12m/s)/3sa = 4m/sa = 4m/s22

C) AccelerationC) AccelerationA student is walking at 2m/s. Something A student is walking at 2m/s. Something shiny flies by and the student takes off shiny flies by and the student takes off reaching a final velocity of 6m/s. It takes reaching a final velocity of 6m/s. It takes her 4s to reach this velocity. What is her her 4s to reach this velocity. What is her acceleration?acceleration?

a = (vf-vi)/∆ta = (6m/s-2m/s)/4sa = (4m/s)/4sa = 1m/s2

D) Acceleration Due to GravityD) Acceleration Due to GravityGravity is a force felt on all Gravity is a force felt on all objects.objects.

It pulls objects towards one It pulls objects towards one another.another.

The earth’s gravity pulls The earth’s gravity pulls everything towards the everything towards the center, we feel this as a center, we feel this as a downward pull. downward pull.

The rate at which objects are The rate at which objects are pulled towards the earth is pulled towards the earth is the same. the same.

D) Acceleration Due to GravityD) Acceleration Due to Gravity

All objects are pulled at the same All objects are pulled at the same rate.rate.

Therefore, acceleration downwards Therefore, acceleration downwards for all objects is the same.for all objects is the same.

Acceleration due to gravity is a set Acceleration due to gravity is a set value of 9.8m/svalue of 9.8m/s22

g = 9.8m/sg = 9.8m/s22

D) Acceleration Due to GravityD) Acceleration Due to GravityA student is thrown from the top of A student is thrown from the top of Prep. The student is at rest on the Prep. The student is at rest on the roof. The flight is 4s long. With what roof. The flight is 4s long. With what velocity do they hit the ground?velocity do they hit the ground?

a = (vf-vi)/∆t

9.8m/s2 = (vf-0m/s)/4s

9.8m/s2 = (vf)/4s

39.2m/s = vf