Starter (2 minutes): A cyclist who has been travelling at a steady speed of 4.0 ms-1 starts to accelerate. If he accelerates at 3.0 ms-2, how long will he take to reach a speed of 12 ms-1?

Scalar Quantities & Vector Quantities

Think about this… There is an empty box, Mr Chu and Josh. If Mr Chu puts 40 apples inside the box and Josh also puts 40 apples inside the same box, what is the total number of apples in the box? If Mr Chu pushes the box with a 40 N of force and Josh also pushes the same box with a 40 N of force, What is the total force applied on the box?

Scalar = size only Vector = size + DIRECTION

Think about this too Mr Chu is driving. He travels 4 km North then 4 km East. What is the total distance Mr Chu travells in his car? What is the total displacement of Mr Chu in his car?

Distance & Displacement Distance is a scalar quantity because it involves the size only and not the direction. Displacement is a vector quantity because it involves both size and DIRECTION.

Scalar or Vector? Distance Displacement Speed Velocity Acceleration Energy Force Temperature Mass Work Power Momentum

When dealing with problems which involve vector quantities (e. g When dealing with problems which involve vector quantities (e.g. calculating velocity, force, etc.), you must consider the size and direction. Which means: YOU MUST USE VECTOR CALCULATIONS and/or VECTOR DIAGRAMS.

A car is driven 3 km east for 200 seconds, then 4 km south for 250 seconds, then 3 km west for 150 seconds. What is the total distance the car has travelled? What is the total displacement of the car? What is the average speed of the car? What is the average velocity of the car?

Average Speed= Total Distance Total Time Average Velocity= Total Displacement Total Time

Speed & Velocity Speed is a scalar quantity because it only involves the size only and not the direction of the movement. Velocity is a vector quantity because it involves both size and direction of the movement.

A car is travelling at 17 ms-1 towards North A car is travelling at 17 ms-1 towards North. It turns around a corner and travels at 17 ms-1 towards West. Did the car’s speed change? Did the car’s velocity change? Did the car accelerate*?

Speed = “how fast” (Scalar) Velocity = “how fast AND in what direction” (Vector) “Constant speed” = moving at the same speed “Constant velocity” = moving at the same speed and in the same direction as well (i.e. in a straight path)

Also think about this: How long is 40 cm? How long is -40 cm? How fast is 2 ms-1 ? How fast is -2 ms-1 ? Sometimes we use the negative sign as an indication of the direction – e.g. “backward” or “downward”

Activity 8A

A cyclist travels 70 m west in 7 seconds, then 40 m north in 5 seconds, then 70 m east in 6 seconds, then 20 m north in 3 seconds. Calculate the total distance Calculate the total displacement Calculate the average speed Calculate the average velocity