MOTION

How can you tell if something is in motion? It is changing position How can you tell if something is changing position Section 2.1

Is my desk in motion? Moving about 1,000 miles an hour due to the rotation of the earth.

Note solar system not to scale

Our approximate location in the Milky Way Galaxy

Our “local group” of galaxies

Motion is always judged relative to something else You are driving driving 55 mph The car ahead of you is moving away at 10 mph The earth is moving in a circle The universe is expanding You have your foot on the brake but the car next to rolls back

Relative Motion Applet What would be different if you were stationary and everything was moving toward you?

Describing motion How could you describe the motion of an object? SPEED

Describing motion How could you describe the motion of an object? Direction

Describing motion How could you describe the motion of an object? Speeding up, slowing down, constant speed

Describing motion How could you describe the motion of an object? Straight Line Path Turning

1 st we will look motion in a straight line at a constant speed

Describing motion How fast it is going (speed) Is it moving straight or turning Is it speeding up, slowing down, or moving at a constant speed What direction it is headed

RATE how would you describe somebody’s rate of eating hotdogs 1 hot dog / day 5 hot dogs / min

A rate is how quickly something happens Something time 5 hot dogs min

How would you find the RATE at which a person moves? 1 m2 m 3 m Distance Time

SPEED = Is the rate at which an object moves Distance Time m s km hr mile hr m kg WHICH OF THE UNITS BELOW COULD REPRESENT SPEED

The person travels 6 m in 3 seconds. What was their speed? 1 m2 m3 m4 m5 m6 m Speed = 6 m 3 s Speed = distance time = 2 m/s start 0 m end

Their rate of movement is a constant 2 m/s. 1 m2 m3 m4 m5 m6 m start 0 m end 3 s How far did they go in the 1 st second?

Their rate of movement is a constant 2 m/s. 1 m2 m3 m4 m5 m6 m0 m end 3 s How far did they go in the 2 nd second?

Their rate of movement is a constant 2 m/s. 1 m2 m3 m4 m5 m6 m0 m end 3 s How far did they go in the 3 rd second?

Their rate of movement is a constant 2 m/s. How far would he travel in 10 seconds? 1 m2 m3 m4 m5 m6 m0 m

Two people travel for 2 seconds, who has the greater speed? 1 m2 m3 m4 m5 m6 m0 m 1 m2 m3 m4 m5 m6 m0 m 1 m/s 3 m/s

Two people travel a distance of 4 m 1 m2 m3 m4 m5 m6 m0 m 1 m2 m3 m4 m5 m6 m0 m 8 m/s 4 m/s Gets there in 0.5 s Gets there in 1 s

SPEED Your speedometer in your car reads 55 mph. What does this mean? 55 miles per hour 55 hr mi Section 2.2

60 hr mi You drive at a constant speed of 60 miles per hour How far did you go after 2 hours How far did you go after 1/2 hours

1 person travels 55 miles in 1.0 hour. Another travels 110 miles in 2.0 hours. Who was moving faster? 110 mi 2.0 hr 55 mi 1.0 hr

time distance Speed = Change in time Change in position Speed =

A River DELTA Means change

Initially the time is 15 seconds and then it is 63 seconds. What is the change in time?  t= t 2 – t 1 Final Initial

Change in time Change in distance Speed = d 2 – d 1 t 2 – t 1 d d = t t Avg =

You are driving and pass mile marker 124. When you pass mile marker 153, you note that 41 minutes has passed. What is your speed? 124 mi 153 mi

Speed = Distance Time A slug slithers for 25 seconds moving along at a pokey 4.6 mm/s, how long is its slime trail?

A student run down the hall at 1.4 m/s, to their classroom which is 38 m away. How long does it take him to get to class?

Driving along the Autobahn at 185 km/hr, how far do you travel in 23 seconds?

You drive 392 km on a road trip and it takes you 5.6 hours. Your average speed is 70 km/hr Why is this only the average speed?

Your speed changes a lot over a trip, distance / time is just an average

Average Speed = distance time Instantaneous speed: your speed at a given moment in time

What does a speedometer tell you? Average Speed or Instantaneous Speed

Which car has the greater average speed? SAME! AVERAGE SPEED

If you move at a CONSTANT speed, then your average speed and instantaneous speed will be the same

There are many different ways to represent motion Words Pictures equations graphs

Motion Diagrams- A picture or dot is placed at regular time intervals to show the location of the object Constant Speed Depicted 1s 2 m Each time interval, Mr. B translates 2 m Motion diagram applet

1s 2 m Each time interval, Mr. B travels 2 m Speed = distance time 2 m 1 s =2 s = m 16 m 8 s =2 s = m

What would change if I was walking slower

What is Mr. B doing?Speeding up Each Flash is 1 sec 1 m1.5 m2 m2.5 m What is the average speed?

Each Flash is 1 sec What is Mr. B doing?Slowing down 1 m1.5 m2 m2.5 m

What is Mr. B doing? slowing down then speeding up

Motion diagrams for different accelerations

You are driving 55 mph. ? But which way

Scalar- just indicates magnitude TWO TYPES OF MEASURMENTS Vectors - indicates magnitude and direction 30 cm55 mph 35 mph West 65 km North

Which would make sense as a vector? (having a direction associated with it) Distance Mass Temperature Speed Time Force

Speed and Velocity are similar BUT Velocity is a vector (has a direction) Speed is a scalar

SPEED 12 m/s VELOCITY 12 m/s East

What changes Speed Velocity You slow down You speed up You make a turn without slowing BOTH CHANGE ONLY VELOCITY CHANGES

CONSTANT SPEED, but velocity is changing DIRECTION of Velocity

In order to move at a constant velocity you must move in a straight line at a constant speed.

Distance is how much you changed your position 1 m2 m3 m4 m5 m6 m0 m Distance traveled is 3 m

Displacement is how much you changed your position & which way 1 m2 m3 m4 m5 m6 m0 m Displacement is 3 m East

By “physics” definition Distance is a scalar (like speed) Displacement is a vector (like velocity) There are some other differences but we won’t discuss them in this class. I walked 25 m I walked 25 m East

If you drive 8.0 m/s North for 4.0 seconds what is your displacement?

Another way to show direction is the sign (+ or -) on a number. In everyday life, direction is given using words like Left, Up, East

Another way to show direction is the sign (+ or -) on a number. (think graphs) Which way is +X Which way is -X Which way is +YWhich way is -Y +X-X +Y -Y

Displacement = x 2 – x 1 final position initial position To show a change a delta is used,  SO Displacement =  x = x 2 – x 1 If you were standing on an X-Axis

initial

And then walked 2 meters to the right 0 m 1 m2 m-1 m-2 m initialfinal Displacement =  x = x 2 – x 1 = 2 m – 0 m = +2 m

The POSITIVE sign means you went to the right. (displacement has direction) 0 m 1 m2 m-1 m-2 m initialfinal Displacement =  +2 m

Because if you were again at zero initial

And then walked 2 meters to the left 0 m 1 m2 m-1 m-2 m initialfinal Displacement =  x = x 2 – x 1 = -2 m – 0 m = -2 m

Find the distance and displacement 0 m 10 m20 m30 m40 m 50 m60 m70 m80 m90 m100 m x StartFinish Displacement = x 2 – x 1 final initial

Find the distance and displacement 0 m 10 m20 m30 m40 m 50 m60 m70 m80 m90 m100 m x StartFinish Displacement = x 2 – x 1 Displacement = 40 m - 0 m = 40 m Is this a vector?????What is the distance?

Find the distance and displacement 0 m 10 m20 m30 m40 m 50 m60 m70 m80 m90 m100 m x StartFinish Displacement =80 m - 20 m = 60 m

Find the distance and displacement 0 m 10 m20 m30 m40 m 50 m60 m70 m80 m90 m100 m x StartFinish Displacement =30 m - 60 m = - 30 m The negative sign indicates movement to the left on this system

-50 m -40 m-30 m-20 m-10 m 0 m10 m20 m30 m40 m50 m x Start Finish Displacement = Distance =

-50 m -40 m-30 m-20 m-10 m 0 m10 m20 m30 m40 m50 m x Start Finish Displacement =-20 m - 0 m = -20 m

In physics we can change what direction we call positive, to make a problem easier. BUT there is a “Standard” way of going it.

+X, Right-X, Left -Y, Down +Y, UP

Speedhow fast Velocity how fast which way scalar vector 5 m/s 5 m/s, S V y = -5 m/s what it iswhat it tells you

IT’S THE SAME EQUATION velocity = displacement time speed = distance time Includes a direction No direction

Average Velocity v = xx tt

If you travel the distance below in 12 sec what is your velocity? 0 m 10 m20 m30 m40 m 50 m60 m70 m80 m90 m100 m x Start

-50 m -40 m-30 m-20 m-10 m 0 m10 m20 m30 m40 m50 m x Start What does the negative sign mean? If you travel the distance below in 5.0 sec what is your velocity?

Velocity and displacement have the same direction! If you moved east, both you displacement and velocity were east If you moved in the +X direction, both displacement and velocity are positive

Velocity will have the same direction as displacement Will the velocity be positive or negative? -50 m -40 m-30 m-20 m-10 m 0 m10 m20 m30 m40 m50 m x Negative

-100 m -90 m-80 m-70 m-60 m -50 m-40 m-30 m-20 m-10 m-0 m x Will the velocity be positive or negative? Positive

A car has an initial position at the +31 m mark, and travels at +3.0 m/s for 5.0 seconds. What is its final position? Note: that positives are usually left off. Also it is assumed that the car is traveling on the x-axis

A car has an initial position at the +31 m mark, and travels at -3.0 m/s for 5.0 seconds. Where does it end up?

Now what is Acceleration When you accelerate, your velocity changes Speeding up Slowing down Changing Direction Section 2.4

vv tt a = Acceleration is the RATE at which velocity changes. The greater the acceleration, the more quickly your velocity changes

vv tt a = Acceleration is the RATE at which velocity changes. Note: if you are NOT turning then …  speed tt a = This is the case, this semester

vv tt a = v 2 – v 1 t a = Since we usually say how much time has passed Solving for v 2 …

v 2 – v 1 t a = v 2 = v 1 + a t A useful form of the equation. Note often the line above “a” is often left off because we will ALWAYS deal with average acceleration.

Which car has the greater acceleration?

ANYTIME you accelerate, you can feel a force. “Flooring” the gas pedal Hitting the brakes Turning the steering wheel.

vv tt a = You hit the gas and go from rest to 15 km/hr in 1.0 seconds. What is your acceleration?

Time (s) Velocity 0 km/hr 5 km/hr 10 km/hr What is the objects acceleration?

A car speeds up from 15 m/s to 40 m/s in 5 seconds. What is its acceleration? UNITS?

vv tt a = What are possible units of acceleration s m s 1 s 1 s x m s2s2 = speed time

Velocity is the rate at which position changes XX tt +55 miles per hour means your position changes by 55 miles every hour (in the + direction) Acceleration is the rate at which velocity changes VV tt +10 m/s per second means That your velocity changes by +10 m/s every second

An object initially at rest experiences a constant acceleration of 6 m/s 2. Time (s) Instantaneous Velocity (m/s)

If an object initially moving at 10 m/s experiences a constant acceleration of 4 m/s 2. Time (s) Instantaneous Velocity (m/s)

What is the cars acceleration? Time (s) Instantaneous Velocity (m/s)

A car initially is moving at 4.0 m/s. It accelerates at a rate of 2.0 m/s 2 for 6.0 seconds. How much does the velocity change? What is the final velocity?

How long will it take a car to go from 25 m/s to 55 m/s, if it accelerates at 5 m/s 2 ?

A car is moving at 58 m/s at time zero, and opens the chute. The car comes to a stop 38 seconds later, what is the acceleration? a = v 2 -v 1 t 2 -t = m s 0 m s s0 s = -1.5 m s2s2 Why negative??? v + a -

If an object initially moving at +10 m/s experiences a constant acceleration of -5 m/s 2. Time (s) Velocity (m/s) WHAT HAPPENED to the object?

0 m1 m2 m3 m4 m Velocity is + or - What will happen to its speed if it experiences a positive acceleration? Acceleration +

0 m1 m2 m3 m4 m Velocity is + or - What will happen to its speed if it experiences a positive acceleration? Acceleration +

0 m1 m2 m3 m4 m Velocity is + or - What will happen to its speed if it experiences a Negative acceleration?

0 m1 m2 m3 m4 m Velocity is + or - What will happen to its speed if it experiences a Negative acceleration? Acceleration -

0 m1 m2 m3 m4 m Velocity is + or - What will happen to its speed if it experiences a positive acceleration? Acceleration +

0 m1 m2 m3 m4 m Velocity is + or - What will happen to its speed if it experiences a positive acceleration? Acceleration +

0 m1 m2 m3 m4 m Velocity is + or - What will happen to its speed if it experiences a Negative acceleration? Acceleration -

0 m1 m2 m3 m4 m Velocity is + or - What will happen to its speed if it experiences a positive acceleration? Acceleration -

WHENEVER the SIGNS (direction) of velocity and acceleration are the SAME, the object speeds up. If signs are opposite the object SLOWS.

A car initially is moving at 5.6 m/s. It accelerates at a rate of -1.1 m/s 2 for 6 seconds. What is its final velocity?

What is the final velocity of a car which has an initial velocity of -32 m/s after it accelerates at +6.0 m/s 2 for 4.0 seconds?

What is the acceleration of a car which is driving a constant 320 km/hr on a straight road for 10 seconds?