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

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

Other units commonly used to express speed… Kilometers per hour, feet per second, miles per hour

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 / t S = 100 m / 20 s S = 5 m/s

The pitcher’s mound in baseball is 85 m from the plate. The balls average speed is m/s. How long does it take for a pitch to reach the plate? Let’s Try: t = d / s t = 85 m / m/s t = 4 s

Now it’s time for the ANIMAL RACE

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.

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.

Can you describe what is happening here? CHANGING SPEED

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

An objects velocity is constant ONLY if its speed and direction don’t CHANGE

Which of the following are examples of velocity? a) 25 m/s forward b) 1,500 km/hr c) 55 m/h south d) All of the above Letters a and c are examples of velocity

Resultant Velocity: The combination of two or more velocities.

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

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

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!

Acceleration: the rate at which velocity changes. Acceleration = final velocity – initial velocity time it takes to change velocity Units for acceleration: m/s 2

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/s 2

Acceleration = 0 m/s – 45 m/s 5 s Acceleration = -9 m/s 2 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? Acceleration in which velocity increases: POSITIVE ACCELERATION Acceleration in which velocity decreases: NEGATIVE ACCELERATION

Can you describe what is happening here? Velocity stays the same: NO ACCELERATION (CONSTANT VELOCITY!)

Can you describe what is happening here? CHANGING ACCELERATION