Motion

What Do We Mean By Speed?

• Exactly how fast are you running?• How many meters do you run for

each second?• Do you always run the same number

of meters each second?

Speed

• The speed of an object is a measure of how quickly the object gets from one place to another.

• Speed is calculated by taking the distance traveled by the time taken.

• Speed = distance/time V = d/t

Distance Verses Displacement

• Distance is how far an object has moved from it’s original starting point.

• Displacement is the distance and direction of an object’s change in position from the starting point.

• http://www.absorblearning.com/media/item.action?quick=4n

Forms of the Speed Equation

Equation Gives you… If you know…

v = d/t Speed time and distance

d = vt Distance speed and time

t = d/v time distance and speed

Velocity

• Velocity is the quantity describing both speed and direction.

• Velocity = distance/time in a specific direction

• Velocity can change without the speed changing.

• What is the velocity of a car that traveled a total of 70 kilometers south in 1.2 hours?

• What is the speed of a jet plane that travels 528 meters in 4 seconds?

• A car is traveling 110 km/hr. How many hours will it take to cover a distance of 725 km?

• How many seconds will it take for a satellite to travel 450,000 m at a rate of 120 m/s?

• How far, in meters, will you travel in 180 seconds running at a rate of 6 m/s?

• The earth travels at 68,000 miles/hour as it moves around the sun. How many miles does the earth travel in one trip around the sun (8760 hrs)?

Acceleration

• Acceleration is the rate of change in velocity. If either speed or direction changes, the velocity will change.

• Acceleration can occur through a change in speed or change in direction.

Acceleration (2)

• Acceleration can be positive or negative. When a car comes to a stop, this is called deceleration.

The speed is decreasing, so the acceleration is

negative.

The speed is increasing, so the

acceleration is positive.

Acceleration Formula

• a = (v2 – v1)/time or

• a = (vf – vi)/time

• v2 or vf is the final velocity

• v1 or vi is the beginning or initial velocity.

What Does an Acceleration Value Tell You?

• If the acceleration is small, that means the speed is increasing very gradually. If the acceleration has a greater value, the object is speeding up more rapidly.

• If an object has zero acceleration, then it is traveling at a constant speed in one direction.

Acceleration Practice Problem

• If a car is traveling at a speed of 40 m/s and stops within 2.5 s, what is the car’s acceleration?

• V1=

• V2=

• T=• A=

Acceleration Practice Problem

• Susan stops a ball and 2 seconds later the ball has a speed of 20 m/s. What is the ball’s acceleration?

• V1=

• V2=

• T=• A=

Acceleration Practice Problem

• John goes over the top of a hill at a speed of 4 m/s while on his bike. Four seconds later his speed is 24 m/s. What is his acceleration?

• V1=

• V2=

• T=• A=

Acceleration Practice Problem

• Sally places a ball at the top of a ramp and lets it go. Four seconds later the ball is moving at a speed of 2.4 m/s. What is the acceleration?

• V1=

• V2=

• T=• A=

Acceleration Practice Problem

• Dave is traveling at 20 m/s in a car when it hits a tree. Dave comes to a complete stop in 4 seconds. What is his acceleration?

• V1=

• V2=

• T=• A=

Acceleration Practice Problem

• A cart rolling down an incline for 5.0 seconds has an acceleration of 4.0 m/s2. If the cart has a beginning speed of 2.0 m/s, what is the final speed?

• V1=

• V2=

• T=• A=