Physics Chapter 2 NotesSpeed, Velocity, and Acceleration

Displacement• The distance in a straight line in a certain direction from the

starting point• Eg Lily walked 1km to the North, then 2km to the East

followed by 1km to the south.• a. what is her total walking distance?• b. what is her final displacement?

• Answers:• a. 1 + 2 + 1 = 4km• b. 2m due east from starting point

Speed and Velocity• Scalar: has only magnitude and no direction• Speed is distance travelled by a body per unit time

• Vector: has both magnitude and direction• Velocity is distance travelled per unit time in a stated direction

• Units: ms-1 or kmh-1

• Average speed is NOT the constant speed

• Instantaneous speed: the speed at any instant• Use speedometer to find instantaneous speed• Can be found by finding the gradient of the tangent to the

displacement-time graph, at that point in time

Speed measurement using ticker-tape timer

Acceleration• Defined as the rate of change of velocity with time

• Units: ms-2 or kmh-2

• If velocity is constant, acceleration= 0• If velocity decreasing negative acceleration/deceleration• The gradient of a velocity-time graph of a moving object gives

the acceleration of the object at a given time

Acceleration of bodies falling near to earth• An object falling near to Earth, where the air resistance is

negligible, has a velocity-time graph that is s straight line. It falls with a constant acceleration

• The only force acting on the object experiencing free fall is the force of gravity

• Acceleration = 10ms-2

Acceleration-time graphs

Decreasing acceleration Decreasing speed Constant speed

Velocity-time graphs

Increasing acceleration Constant acceleration

Zero accelerationConstant speedConstant speed

Distance-time graph

Area under velocity-time graph• Area under velocity-time

graph is the distance