CHAPTER 11

Motion

Distance and DisplacementTo describe motion accurately and completely

a frame of reference is necessary.

Frame of Reference: a system of objects that are not moving with respect to one another

Relative Motion: the movement in relation to a frame of reference Example: a train moves past the train station

Measuring DistanceDistance: the length of a path between two

points The SI unit is meter (m) 1 kilometer equals 1000 meters One centimeter equals one hundredth of a meter

Measuring Displacements

Displacement: the direction from the starting and the length of a straight line from the starting point to the ending point

Involves distance and direction

Combining Displacements

Vector: a quantity that has magnitude and direction

Key Point: Add displacements using vector addition

If vectors are in the same direction you ADD them.If vectors are in opposite directions you SUBTRAC

them

Resultant Vector: the vector sum of two or more vectors

Speed and Velocity

Speed: the ration of the distance an object mores to the amount of time the object moves

The SI unit of speed is meters per second (m/s)

Average vs. Instantaneous Speed

Average Speed Computed for the

entire duration of a trip

Formula is total distance

total time

Speed = d/t

Instantaneous Speed Measured at a

particular instant

The speed you are going right now

VelocityKey point: a description of both speed and

direction of motion. Velocity is a vector. (Speed is not)

You combine velocities the same way you combine displacements.

Same direction = add Opposite direction = subtract

Speed and Velocity Graphs

Description: going at a constant speed

Description: going at a constant speed then stopped

Math Time V=d/t

1. Calculate the average speed of a person that run 45 m in 7 second.

2. How long would it take to travel 400 km at a speed of 60 km/hr?

3. A train travels 190 km in 3.0 hours and then 120 km in 2.0 hours. What is it’s average speed?

Acceleration

Acceleration: the rate at which velocity changes

Can be described as changes in speed, changes in direction or both

Acceleration is a vector

Formula for acceleration is:change in velocity or Vf – Vi Total time t

Unit is (m/ss)

Acceleration Graphs

Key to remember: velocity (speed) on y –axis, time on the x –axis!!

Description: Constant acceleration

Description: constant acceleration, constant speed, acceleration

Description: accelerating, constant speed, deceleration