Physics Chapter 3 Describing Motion

3.1 Picturing Motion Motion diagram Operational definition Particle model 3.2 Where and When Coordinate systems Scalar/Vector quantities Displacement Time interval 3.3 Velocity and Acceleration Velocity (average/instantaneous) Speed Average acceleration Problem Solving Strategies

3.1 Picturing Motion When studying moving objects it is useful to understand their motion by picturing how that motion would look. FAST OR SLOW

Motion Diagram A series of images of a moving object that records its position after equal time intervals.

Operational Definition of Motion Before we describe motion mathematically we will study motion in terms of a procedure or operation used to identify it. This is called an operational definition.

Motion Diagram For the next four slides the time between images is 1 second. How would you describe the following motion?

Motion Diagram For the next three slides the time between images is 1 second. How would you describe the following motion?

Motion Diagram For the next two slides the time between images is 1 second. How would you describe the following motion?

Motion Diagram For this slide the time between images is 1 second. How would you describe the following motion?

Motion Diagram Particle Model—instead of using objects we can replace them with a single point. This helps to eliminate extraneous motion

3.2 Where and When? When studying motion it is important to be able to locate the object that you are studying. You also may need to be able to decide if it is moving.

Frame of Reference To make position measurements of an object you must choose a reference frame and a reference point that is defined to be stationary and at point zero. The wain

Coordinate System Once a reference frame has been determined objects can be located within it by establishing a coordinate system Coordinate system—tells you the zero point (origin) and direction of change in the variable you are studying. Motion in 2 directions Y-axis X-axisOrigin

Vector An arrow that represents the magnitude and direction of a quantity Position vector Shows the position of an object relative to the origin Direction and distance Example: 2.5m east 2.5m east

Scalar/Vector Quantities Scalar Quantities Tell only the magnitude of the measurement Examples: Time Temperature Mass Distance Speed Vector Quantities Tell both magnitude and direction of the measurement Examples: Displacement Velocity Acceleration

Distance/Displacement Distance Scalar quantity The length of the path an object takes. Displacement Vector quantity The change it position between an object’s starting position and the ending position Distance + direction

Distance/Displacement So what’s the difference between distance and displacement? Total distance traveled Total displacement 5m 4m

Displacement  d = d 1 – d o  d (displacement)= d 1 (ending position) – d o (starting position)

Time Since time is the separation between the occurrence of two events, it is better in physics to talk about the time interval in which something occurs.

Time Time interval (  t) The difference between starting time (t 0 ) and ending time (t 1 ) for an occurrence.  t = t 1 – t o

3.3 Velocity and Acceleration In your own words define the physics term velocity. How is it different from speed?

3.3 Velocity and Acceleration What is average velocity and what is its symbol?

3.3 Velocity and Acceleration Write the equation for calculating average velocity. Define all terms.

3.3 Velocity and Acceleration Explain the difference between average velocity and average speed.

3.3 Velocity and Acceleration Explain the difference between average velocity and instantaneous velocity.

3.3 Velocity and Acceleration Explain why we cannot use the equation, v = (d 1  d o )/  t to solve for instantaneous velocity.

3.3 Velocity and Acceleration Show how the equation, v =  d/  t can be rearranged to find displacement given average velocity and time.

3.3 Velocity and Acceleration Show how the equation, v = (d 1  d o )/  t can be rearranged to find final position given average velocity, initial position and time.

3.3 Velocity and Acceleration Explain how the velocity 15m/s is the same as  15m/s and how it is different.

3.3 Velocity and Acceleration In your own words, define acceleration.

3.3 Velocity and Acceleration What is average acceleration and what is its symbol?

3.3 Velocity and Acceleration Write the equation for calculating average acceleration. Define all terms.

3.3 Velocity and Acceleration Under what set of conditions is acceleration positive and under what set negative?

In conclusion………………… Let check our knowledge!

Magnitude + Direction Measurement Quantities Scalar Vector Distance Speed displacement Velocity Acceleration