SPH 4U1

Unit 2: Kinematics (How Things Move)

Note 2: Speed and Velocity

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Reference Text Section 1.1

Recall Definitions:

Scalar – magnitude and a unit (no direction)- time, distance, speed

Vector – point of reference, magnitude, unit & direction – positions, displacement, velocity

Speed – rate of change of distance with time

Displacement – the change of positions (final position – the intial position)

Velocity – rate of change of position with time

Instantaneous Velocity – speed at one point in time together with the direction it is moving in at that time.

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Example 1: A person jogs around a circular 800m track in 6 minutes.  Calculate

(i)                  the average speed

(ii)                the average velocity

Solution: Convert 6 minutes to seconds 6.0 min.* 60.0 s/min. = 360.0 s

(i)                  average speed =

(ii)                average velocity =

Example 2: A clock has a 2nd hand that is 12.0 cm long.  Find the following:

(i)                  Average speed of the tip of the 2nd hand

(ii)                Instantaneous velocity as it passes the 6 & 9 on the clock face

(iii)               Average velocity in moving from the 3 to the 12 on the clock

Solution:

(i)

(ii)    (recall inst velocity is speed & dir’n at that point in time)

Speed is constant so

Answer: As it passes the 6 the inst. Velocity is 1.3 cm/s [LEFT]

Answer: As it passes the 9 the inst. Velocity is 1.3 cm/s [UP]

(iii)  Find the displacement of the 2nd hand from 3 to 12

Do Section 1.1 Questions Page 17