SPEED, VELOCITY AND ACCELERATIONMotion

Distance & Displacement

Frame of Reference• Motion: a change in position relative to a frame of

reference• Frame of Reference: The object or point from which

movement is determined.• A system of object that are not moving with respect to one another.

Must have a frame of reference to determine motion.

Choosing a Frame of Reference• Relative Motion: movement in relation to a frame of

reference.

• Most common frame of reference is Earth.• Choose a frame of reference that allows you to more

accurately describe motion.

Distance• Distance: The length of a path between two points

• SI unit: meter (m)• Can use kilometer (km) or centimeter (cm)

Displacement• Displacement: the direction from the starting point and the

length of a straight line from the starting point to the ending point• Includes distance and direction• Example of a vector (has both magnitude & direction)

• Example:• Distance: the girl walked 5 blocks• Displacement: the girl walked 5 blocks east

Combining Displacements• Add displacements using Vector addition

• Straight line• If 2 displacements are in the same direction-add vectors• If 2 displacements are in the opposite direction-subtract

vectors

• Not straight line• Need to combine by graphing…creating a Resultant

vector

SEC. 11.2Speed & Velocity

Speed• Speed: the ratio of the distance an object moves to the

amount of time the object moves

• Speed = Distance or s = d Time t

• SI unit: meter/second (m/s)

Types of Speed• Average Speed: the total distance traveled divided by

the time it takes to travel that distance• Ex. Average speed over an entire trip

• Instantaneous speed: the rate at which an object is moving at a given moment in time• Ex. Speed at a given moment

Graphing Constant Speed

• Speed = Slope of the line

Graphing Varying Speed

• Speed is changing...so, slope for each section is the speed for that time

Velocity• Velocity: description of both speed and direction of

motion• Velocity is a vector (can be added like vectors)

• Velocity = displacement or v = d time t

• SI unit: m/s

Acceleration

Acceleration• Acceleration: rate at which velocity changes

• Change in speed, direction or both

• Deceleration: negative acceleration• an object slows down

• Constant acceleration: a steady change in velocity

Change in Speed

• Occurs when an object speeds up or slows down• Direction is constant

• Ex. Free fall: the movement of an object toward Earth due to gravity

Change in Direction

• Occurs when an object changes direction• Speed is constant

• Ex. Riding a carousel• Ex. Riding a Ferris wheel

Change in Speed & Direction

• Occurs when there is a change in both speed and direction

• Ex. Riding a roller coaster

Calculating Acceleration• Change in velocity divided by the total time

• Acceleration = (vf – vi)

tvf: final velocity

vi: initial velocity• SI unit: m/s2

Graphing Acceleration

• Acceleration = slope of the line