1. Mr. Conkey Physical Science Ch. 11
Motion
Mr. Conkey Physical Science Ch. 11

2. Distance and Displacement
Choosing a frame of reference
To describe motion accurately and completely, a frame of reference is needed
Frame of reference – a system of objects that are not moving with respect to one another

3. How fast are you moving?
Relative motion – movement in relation to a frame of reference
Which frame to choose?
Depends on what you
are measuring.

4. Measuring Distance Distance – the length of a path between two points
length of path from the starting point to the ending point
SI unit for measuring distance = meter (m)
Large distance = (km); shorter = (cm)

5. Measuring Displacements
Displacement – the direction from the starting point and the length of a straight line from the starting point to the ending point
Displacement is an example of a vector

6. Combining Displacements
Vector – a quantity that has magnitude and direction
Magnitude can be amount, length, or size
Add displacements using vector addition (the combining of vector magnitudes and directions)

7. Combining Displacements (cont.)
When combining displacement vectors along a straight line, vectors can be added or subtracted
Figure A shows vector addition, figure B shows vector subtraction.

8. Displacement Not Along a Straight Path
Resultant vector – the vector sum of two or more vectors
What is the resultant vector for the image to the right?
Formula for the hypotenuse of a right triangle = a² + b² = c² ; rearranged it is c = 𝑎 2 + 𝑏 2 So, = 50 𝑚

9. Try this example
A child walks from her home to school travelling north and east.
What is the total distance the child walked?
What is the total displacement in blocks?

10. Speed and Velocity
Speed – the ratio of the distance an object moves to the amount of time the object moves
SI unit for speed is meters per second
Average speed – measured for the entire duration of the trip
Instantaneous speed – measured at a particular instant
As with distance, speed measurement is relative to what you are talking about; meters per second versus kilometers per hour

11. Average Speed Average speed = Total distance Speed Variations
Total time
Speed
Variations

12. Sample Problem
You took a family vacation and travelled 35 kilometers in 0.4 hours, and then another 53 kilometers in 0.6 hours. What is your average speed?

13. Instantaneous Speed
Instantaneous speed – the rate at which an object is moving at a given moment in time
Graphing motion
The slope of a line on a distance – time graph is speed

14. Velocity Velocity – The speed and direction of a moving object
Velocity is a vector
Two or more velocities add by vector addition

15. Acceleration
Acceleration – changes in speed, direction, or both (velocity)
Acceleration is a vector
Changes in speed – positive acceleration (increasing) or negative acceleration (decreasing aka deceleration)
Example of acceleration: free fall

16. Acceleration (cont.)
Changes in direction – acceleration can change even if speed is constant (e.g. a carousel)
Constant acceleration – a steady change in velocity

17. Calculating Acceleration
Acceleration can be calculated for straight-line motion by dividing the change in velocity by the total time
Acceleration formula – a is the acceleration (unknown), vi is the initial velocity, vf is the final velocity, and t is the total time

18. Sample Problem
A ball rolls down a ramp, starting from rest. After two seconds, its velocity is 6 meters per second. What is the acceleration of the ball?
Using the formula, a = (6 m/s - 0 m/s) / 2 s ; answer is a = 3 m/s² down the ramp.

19. Ball and Ramp activity
Now lets first calculate the average speed of the marble as it rolls down each of the ramps (sketch the marble and ramp and record each of these average speeds into your notes)
Finally, lets calculate the acceleration of the ball down each of the ramps (again record these into your notes).
Discuss the differences between each ramp(if any) and why you think this is happening.

20. Graphs of Acceleration
The slope of a speed-time graph is acceleration
Linear graph – a graph where the displayed data form straight line parts.

21. Distance-Time Graphs
Nonlinear graph – a curve connects the data points that are plotted
Instantaneous acceleration – how fast a velocity is changing at a specific instant

22. This is the end of chapter 11!!! (wow, that was fast, get it?)