1) What is the relationship between speed, velocity, and acceleration?

2) How do you calculate speed, velocity and acceleration?

3) How can you determine motion from a graph?

Average speed is calculated as distance divided by time.

Equation for Average Speed

speed = distance

time v = dt

• Instantaneous speed is the speed at a given point in time.

Velocity is the speed of an object in a particular direction.

Velocity describes both the speed and the direction.

Combine velocities to determine the resultant velocity.

1) Which of the following examples shows a change in velocity? Remember a change in velocity can be either a change in speed or a change in the direction of motion. Briefly explain your answer.

a. a car coming to a stop at a stop signb. a book sitting on a deskc. a yo-yo in motiond. a bicyclist making a left-hand turn at exactly 15

km/h

2. For which of the following is the velocity constant?

A. a baseball traveling away from a bat after a hitB. a bicyclist on an oval track moving at a constant speed of 15 km/h C. a helicopter hovering motionless above a fixed point on the groundD. a canoe being carried down a winding river by a steady current

3. Mathew takes 45 s to walk eastward along a straight road to a tore 72 m away. What is their average velocity?

v = x/t = 72 m / 45 s = 1.60 m / s eastward

4. How much time does it take for a student running at an average speed of 5.00 m/s to cover a distance of 2.00 km? • Write down formula: V = x / t

• Manipulate equation: t = x / v• Convert numbers to same units:

2.00 km = (2.00 km)(1000 m/1 km) = 2000 m

• Solve: t = 2000 m / 5.00 m/s = 400 seconds

Acceleration is the rate at which velocity changes over time.

An object accelerates if its speed, direction, or both change.

Acceleration is the rate at which velocity changes.Acceleration Equation (for straight-line motion)

acceleration = final velocity – initial velocity

time a = ∆vt

• In SI units, acceleration is measured in meters per second per second (m/s/s) or m/s2.

Acceleration A flowerpot falls off a second-story windowsill. The flowerpot starts from rest and hits the sidewalk 1.5 s later with a velocity of 14.7 m/s. Find the average acceleration of the flowerpot.

1. List the given and the unknown values.Given: time, t = 1.5 s

initial velocity, vi = 0 m/sfinal velocity, vf = 14.7 m/s down

Unknown: acceleration, a = ? (m/s2 and direction)

3. Insert the known values into the equation, and solve.

a = vf – vi

t = 14.7 m/s – 0 m/s

1.5 s

a = 14.7 m/s

1.5 s = 9.8 m/s2 down

acceleration = final velocity – initial velocity

time = vf – vi

t

2. Write the equation for acceleration.

2) In science, which of the following are examples of acceleration?

a) A car speeding up?b) A car breaking for a red light?c) A car driving, down a straight road at 60

mph?d) A car driving around a curve at 60 mph?

(Acceleration occurs whenever and object changes its speed or changes directions. All of the above are examples of acceleration except letter c, which is an example of constant velocity. Letter D is an example of acceleration because the car changes direction as it goes around a curve.)

1. A bicyclist traveling at 10 m/s applies her brakes, reducing her velocity to 5 m/s. If it takes 2 seconds to slow the bike, what is the acceleration during that period?A. –5 m/s2

B. –2.5 m/s2 C. 0 m/s2

D. 2.5 m/s2

Answera = (vf – vt) / t

a =(5 m/s – 10 m/s) / 2 s

a = -5 m/s / 2 s

a = -2.5 m/s

Speed and velocity can be determined from a distance-time graph. When an object’s motion is graphed by plotting distance on the y-axis and time on the x-axis, the slope of the graph is speed. Which line to the right shows greatest speed?

Answer: Cruising Jet, the one with the greatest slope or steepness.

Acceleration can be determined from a velocity-time graph.

The slope of a velocity-time graph gives you acceleration.

1) In the velocity time graph to the right, is velocity increasing, decreasing or constant?

(Decreasing, line is sloping down.)

2) Is acceleration increasing, decreasing or constant?

(Constant, because the slope does not change.)

3. What is the average speed of the runner whose motion is plotted on the graph?F. 1.0 m/sG. 1.9 m/s H. 2.4 m/sI. 4.5 m/s

4. During which interval is the runner’s average speed the greatest?A. 0 s to 5 sB. 5 s to 10 s C. 15 s to 20 sD. 20 s to 25 s

Answer: 3) s = d/t = 48 m/ 25 s = 1.9

m/s 4) C, greatest slope here.

1) Speed (B)

2) Velocity (A, D)

3) Acceleration (C)

** one will have 2 definitions.

A. Speed in a particular direction

B. Change in distance over time

C. The change in velocity over time

D. The change in displacement over time