**10 POINT DIY: Arcola Elementary, has a science fair every year and is in need of some judges. Thursday, March 26.

 The contact at the school is Ms. Jackie Bruley.

jackie.bruley@lcps.org

Bell Ringer

1.What is speed?

2.What would you need to know in order to calculate your own speed?

Unit 6: Force and Motion.

Speed: The rate at which an object moves; speed depends on the distance traveled

and the time taken to travel that distance.

Formula: SI Unit:Meters / second

Unit 6: Force and Motion.

Other units commonly used to express speed…

Kilometers per hour, feet per second, miles per hour

Unit 6: Force and Motion. Let’s Try:

A football field is about 100 m long. If it takes a person 20 seconds to run its length, how fast

(what speed) were they running?

S = d / tS = 100 m / 20

sS = 5 m/s

Unit 6: Force and Motion.

The pitcher’s mound in baseball is 85 m from the plate. The balls average speed is 21.25 m/s. How

long does it take for a pitch to reach the

plate?

Let’s Try:

t = d / st = 85 m / 21.25

m/st = 4 s

Unit 6: Force and Motion.

Now it’s time for the ANIMAL RACE

Unit 6: Force and Motion.

If something is not moving, a horizontal line is drawn on a distance-time graph

Time is increasing to the right, but its distance does not change. It is

STOPPED.

Both are CONSTANT SPEEDS.

A steeper gradient = higher speed.

Unit 6: Force and Motion.

Unit 6: Force and Motion.

Can you describe what is happening here?

CHANGING SPEED.For the first part of the journey, the object

moved at a steady (slow) speed.It then suddenly increased its speed.

Unit 6: Force and Motion.

Can you describe what is happening here?

CHANGING SPEED

Unit 6: Force and Motion.

Velocity: The speed of an object in a particular direction.

An airplanes velocity is 600

km/h

An airplanes velocity is 600 km/h SOUTH

Unit 6: Force and Motion.

An objects velocity is constant ONLY if its speed

and direction don’t CHANGE

Unit 6: Force and Motion.

Which of the following are examples of velocity?

a) 25 m/s forwardb)1,500 km/hrc) 55 m/h south

d)All of the above

Letters a and c are examples of velocity

Unit 6: Force and Motion.

Resultant Velocity: The combination of two or more velocities.

Unit 6: Force and Motion.

If you are riding a bus traveling east at 25 m/s. You stand up and walk down the bus’s aisle at

1 m/s east. What is your RESULTANT VELOCITY?

15 m/s east + 1 m/s east = 16 m/s east

Unit 6: Force and Motion.

If you are riding a bus traveling east at 25 m/s. You stand up and walk down the bus’s aisle at

1 m/s west. What is your RESULTANT VELOCITY?

15 m/s east - 1 m/s west = 14 m/s east

Unit 6: Force and Motion.

When velocities are in the same direction, add them together.

When velocities are opposite direction, subtract them.

*The resulting direction is from the larger velocity!

Unit 6: Force and Motion.

Acceleration: the rate at which velocity changes.

Acceleration = final velocity – initial velocity time it takes to change

velocity

Units for acceleration:

m/s2

Unit 6: Force and Motion.

You are riding your bike down a hill. At point A your velocity is 5 m/s south. 2 seconds later you pass point

B and your velocity is now 25 m/s. What is your acceleration from point A to point B?

Acceleration = 25 m/s – 5 m/s 2 s

Acceleration = 10 m/s2

Unit 6: Force and Motion.

Acceleration = 0 m/s – 45 m/s 5 s

Acceleration = -9 m/s2

You are coming up to a stop sign and start to press on the breaks. 5 seconds from the sign, your velocity is

45 m/s west. Once you reach the sign you have stopped, your velocity is 0 m/s west. What is your

acceleration as you approach the sign?

Can you describe what is happening here?

Unit 6: Force and Motion.

Acceleration in which velocity

increases: POSITIVE ACCELERATION

Acceleration in which velocity

decreases: NEGATIVE

ACCELERATION

Can you describe what is happening here?

Unit 6: Force and Motion.

Velocity stays the same: NO ACCELERATION

(CONSTANT VELOCITY!)

Can you describe what is happening here?

Unit 6: Force and Motion.

CHANGING ACCELERATION