Motion Velocity and Acceleration

Frames of Reference The object or point from which movement is determined The object or point from which movement is determined Movement is relative to an object that appears stationary (does not move) Movement is relative to an object that appears stationary (does not move) Earth is a common frame of reference Earth is a common frame of reference

Questions What is the frame of reference for the sunset? What is the frame of reference for the sunset? What is a frame of reference for reading a map? What is a frame of reference for reading a map? What is the most common frame of reference? 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? 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. Motion is a change in position relative to a frame of reference. Position (d) Position (d) Displacement Displacement Distance Distance Scalar – motion without a direction Scalar – motion without a direction Vector – motion with a direction Vector – motion with a direction

Speed Scalar quantity – No direction; 5 mi/hr. Scalar quantity – No direction; 5 mi/hr. Speed (v) = distance (d) Speed (v) = distance (d) time (t) time (t) Units = Units = meters (m) /second (s) meters (m) /second (s) Kilometers (km) / hour (h) Kilometers (km) / hour (h) Miles (mi) / hour (h) Miles (mi) / hour (h)

Constant Speed Speed that does not change Speed that does not change A straight line on a position - time graph A straight line on a position - time graph Also known as uniform speed Also known as uniform speed

Average Speed Total distance divided by total time Total distance divided by total time V = d 2 – d 1 V = d 2 – d 1 t 2 – t 1 t 2 – t 1

Velocity Speed with a direction; 5 mi / h, southwest Speed with a direction; 5 mi / h, southwest Same formulas are used Same formulas are used Direction can be negative or positive from the frame of reference Direction can be negative or positive from the frame of reference

Velocity Practice Problems Always, always, always set up the chart Always, always, always set up the chart A car takes 25 seconds to go 14 meters. What is the car’s speed? 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? 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 similar? How are speed and velocity the same? How are speed and velocity the same? What determines an objects velocity? What determines an objects velocity? Hoe can you tell from a graph is the velocity is uniform or not? Hoe can you tell from a graph is the velocity is uniform or not?

Acceleration A change in velocity. A change in velocity. The change can be in the speed of motion, in the direction of motion, or both. The change can be in the speed of motion, in the direction of motion, or both. Includes slowing down (deceleration) Includes slowing down (deceleration) Found by calculating the slope on a Velocity vs. Time Graph Found by calculating the slope on a Velocity vs. Time Graph Acceleration (a) = Velocity or Speed (v) Acceleration (a) = Velocity or Speed (v) Time (t) Time (t) Unit is meters/second/second or m /s 2 Unit is meters/second/second or m /s 2

Constant Acceleration Velocity is changing at a constant rate Velocity is changing at a constant rate Also known as uniform acceleration 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 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? 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 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? 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? What is happening between each interval on the graph?

Review Continued? What is a common unit for speed? What is a common unit for speed? What is a common unit for acceleration? What is a common unit for acceleration? How do the y-axis of the graphs for determining speed and acceleration compare? How do the y-axis of the graphs for determining speed and acceleration compare?