Motion, Speed, Velocity, and AccelerationNadia Reese6th grade science

Motion

Motion- when an object changes its position relative to a reference point.

In order to know something has moved, you need to know the point from where it started.

Distance

Distance – how far an object has moved. The SI unit of length is the meter (m). Longer distances are measured in

kilometers (km). Shorter distances are measured in

centimeters (cm).

Time

Time - an instance or single occasion for some event.

The SI unit of time is the second (s). Other units for time are the minute, hour,

days, years, etc…

Speed

Speed – the distance an object travels divided by how long it took (time).

37.5 km/hr

Instantaneous Speed

The speed at a particular point in time. Example-speedometer in car.

Constant Speed

Means that the speed of the object under consideration on NOT changing.

Example-cruise control

Average Speed

TOTAL distance traveled divided by the total time it took.

EXAMPLE: Trip from El Paso to Las Cruces.

Velocity

Velocity– the distance an object travels divided by how long it took (time) in a certain direction.

37.5 Km/hr West

Velocity

The velocity of an object can change even if the speed remains constant.

Ex. going around a curve in cruise control

Calculating Speed/Velocity

V=d/t (distance divided by time) V = Velocity (m/s) d= distance (m) t = time (s)

Example 1

A bicycle rider travels 60.0 km in 3.5 hours. What is the cyclist’s average speed?

Example 2

What is the average speed of the car that traveled a total of 300.0 miles in 5.5 hours?

Graphing Motion

A distance-time graph makes it possible to display the motion of an object over a period of time.

The slope of the line represents the speed. The steeper the slope, the faster the speed.

The horizontal line means that the velocity is zero.

Distance is always plotted on the y- axis and time is always on the x-axis.

Distance-Time Graph

Distance-Time Graph

Distance-Time Graph

Distance-Time Graph

Distance-Time Graph

Distance-Time Graph Questions

What is the speed at B-C? ____________ How far did the car drive before it stopped the

first time? _________ How far did the car drive the whole trip?

___________ How long did the whole trip take? __________ What is the car’s average speed? ___________

Velocity-Time Graph

Acceleration

Acceleration is the rate of change in velocity. When the velocity of an object changes, the object accelerates.

Acceleration occurs when an object changes its speed, direction, or both.

When an object increases it velocity it is called acceleration, when an object decreases its velocity it is called deceleration.

Acceleration Formula

a = Vf –Vi

------------- t

Vf = final velocity (m/s)

Vi = initial velocity (m/s)

a = acceleration (m/s2)t = time (s)

Example 1

A skateboarder is moving in a straight line at a speed of 3m/s and comes to a stop in 2s. What is the skateboarder’s acceleration?

Example 2

A flying doughnut increases its speed from 30m/s to 145 m/s in 11.6 s. What is its acceleration?