Chapter 4 - Motion

Frames of Reference Is this train in motion? How do you know?

Frames of Reference Frames of reference help us to describe the motion of something

Frames of Reference RELATIVE MOTION is movement in relation to a frame of reference.

Frames of Reference Frame of Reference ObjectRelative Motion You – on a moving bus Your friend – in a nearby seat You – on a moving bus Your friend – standing at the bus stop You – standing at the bus stop Your friend – on the moving bus

Measuring Distance Distance is the length between 2 points When measuring the length, be sure to include units (cm, km, m)

Measuring Displacement Displacement is direction + length between starting and ending points

Displacement Along a Straight Line A VECTOR is a quantity the describes size, length or amount, and direction – Same direction = add them – Opposite directions = subtract the difference – Example: Figure 4.2 on page 78

Displacement That Isn’t Along a Straight Path Use graphing to help determine displacement Displacement is always shorter than or equal to the distance

QUICK LAB!!! Using graph paper and rulers, draw a path on your paper with at least 3 turns. Measure the total distance of the path and displacement.

Review! What’s a frame of reference? What’s is distance? How is displacement different than distance?

4.1 Vocabulary Speed Average speed Instantaneous speed velocity

Speed SPEED is the ratio between the distance an object travels to the amount of time is takes Example: 50 miles/hour

Average Speed vs. Instantaneous Speed Average speed = total distance/total time – Formula: s = d/t Instantaneous Speed = how fast something is moving at any given movement – Example: a speedometer in a car measures instantaneous speed

Graphing Motion The slope of a line on a distance-time graph is speed The steeper the slope, the faster the speed! Check out page for comparing graphs!

Velocity Speed in a given direction! Velocities in the same direction are added Velocities in opposite directions are subtracted

4.3 Vocabulary Acceleration Free fall Constant acceleration Linear graph Nonlinear graph

What is acceleration?? Acceleration = rate at which velocity changes Can be described as a change in speed, change in direction, or change in both The rate of acceleration, due to gravity is 9.8m/s/s

Changes in Speed FREE FALL – movement of an object toward Earth solely because of gravity

Changes In Direction You can accelerate even if your speed is constant! Example: the speed may be constant on a carousel, but the direction is always changing

Changes in Speed and Direction Sometimes speed and direction can change at the same time Example: riding a roller coaster!

Constant Acceleration A steady change in velocity The velocity of the object changes by the same amount each second

Calculating Acceleration Acceleration = change in velocity/total time – Formula = (v f – v i ) t Complete the Math Practice problems on page 346

Graphs of Accelerated Motion The slope of a speed-time graph is acceleration Check out pages 86 & 89 for graphing examples!