Motion

Velocity and Acceleration

Frames of Reference The object or point from which

movement is determined Movement is relative to an object

that appears stationary (does not move)

Earth is a common frame of reference

Questions

What is the frame of reference for the sunset?

What is a frame of reference for reading a map?

What is the most common frame of reference?

Question

If you are travelling down the interstate, how can you determine if you are tailing too closely to the vehicle in front of you?

Motion

Motion is a change in position relative to a frame of reference.

Position (d) Displacement Distance

Scalar – motion without a direction Vector – motion with a direction

Speed

Scalar quantity – No direction; 5 mi/hr.

Speed (v) = distance (d) time (t)

Units = meters (m) /second (s) Kilometers (km) / hour (h) Miles (mi) / hour (h)

Constant Speed

Speed that does not change A straight line on a position - time

graph Also known as uniform speed

Average Speed

Total distance divided by total time V = d2 – d1

t2 – t1

Velocity

Speed with a direction; 5 mi / h, southwest

Same formulas are used Direction can be negative or positive

from the frame of reference

Velocity Practice Problems

Always, always, always set up the chart

A car takes 25 seconds to go 14 meters. What is the car’s speed?

A bus travelling at 18 m/s takes 4,200 seconds to complete it’s trip. How far did it travel?

What do you Know?

What are you Finding?

What is your Formula?

Graph Interpretation• What is happening during 0 and 40 seconds?• What is happening during 40 and 70 seconds?• How does the speed between 70 and 90

seconds compare to 90 and 100 seconds?• What is the speed between 10 and 30 seconds?

Hint: Find the slope of the line.

Comparing Lines on a Graph

Review Questions

How are speed and velocity similar?

How are speed and velocity the same?

What determines an objects velocity?

Hoe can you tell from a graph is the velocity is uniform or not?

Acceleration A change in velocity. The change can be in the speed of

motion, in the direction of motion, or both.

Includes slowing down (deceleration)

Found by calculating the slope on a Velocity vs. Time Graph

Acceleration (a) = Velocity or Speed (v)

Time (t) Unit is meters/second/second or m

/s2

Constant Acceleration

Velocity is changing at a constant rate

Also known as uniform acceleration

Non-uniform Acceleration

Acceleration Word Problems

* Use the KFF chart * A roller coaster car rapidly picks up speed as it

rolls down a slope. As it starts down the slope, its speed is 4 m/s. But 3 seconds later, at the bottom of the slope, its speed is 22 m/s. What is its average acceleration?

A cyclist accelerates from 0 m/s to 8 m/s in 3 seconds. What is his acceleration ? Is this acceleration higher than that of a car which accelerates from 0 to 30 m/s in 8 seconds?

Problems Continued…

A car advertisement states that a certain car can accelerate from rest to 70 km/h in 7 seconds. Find the car’s average acceleration.

A lizard accelerates from 2 m/s to 10 m/s in 4 seconds. What is the lizard’s average acceleration?

Review Questions

What is happening between each interval on the graph?

Review Continued?

What is a common unit for speed? What is a common unit for

acceleration? How do the y-axis of the graphs for

determining speed and acceleration compare?