Physics - Term 1 - Week 7

Kinematics is the branch of physics that deals with the motion of objects without considering the forces that cause the motion. In one-dimensional motion, we focus on how an object moves along a straight line. Displacement is the change in position of an object and is a vector quantity, meaning it has both magnitude and direction. Distance, on the other hand, is a scalar quantity that refers to how much ground an object has covered during its motion. Speed is the rate at which an object covers distance, while velocity is the rate of displacement. Acceleration is the rate of change of velocity over time and can be positive (speeding up) or negative (slowing down).

A car travels 100 meters to the east and then 50 meters to the west. To calculate the total displacement, we consider the direction. The displacement is 100 m (east) - 50 m (west) = 50 m (east). This example illustrates how displacement takes direction into account, unlike distance, which would simply be 150 m.

Consider a runner who completes a 400-meter lap in 50 seconds. To find the average velocity, we use the formula: velocity = displacement / time. Here, the displacement is 400 m (the runner ends up where they started), and the time is 50 s. Thus, the average velocity is 0 m/s. Discuss with your peers how this differs from the average speed, which would be 400 m / 50 s = 8 m/s.

Solve the following problems on your own: 1) A car accelerates from rest to 20 m/s in 5 seconds. Calculate the acceleration. 2) A cyclist slows down from 15 m/s to a stop in 3 seconds. What is the cyclist's acceleration? Show your calculations and reasoning.

• Speed is a vector; velocity is a scalar.
• Speed is a scalar; velocity is a vector.
• Both speed and velocity are scalars.
• Both speed and velocity are vectors.

Answer: Speed is a scalar; velocity is a vector.

Speed does not have a direction, while velocity does.

• It is positive.
• It is negative.
• It is zero.
• It varies.

Answer: It is zero.

Constant velocity means there is no change in speed or direction, hence zero acceleration.

Answer: Displacement is the change in position of an object, measured as a straight line from the initial to the final position.

Displacement is a vector quantity that considers direction.

• 100 meters north
• 100 meters south
• 200 meters
• 150 meters

Answer: 100 meters north

Displacement is calculated as 150 m (north) - 50 m (south) = 100 m (north).

Answer: Acceleration = (final velocity - initial velocity) / time.

This formula shows how acceleration is the change in velocity over time.

• Displacement
• Velocity
• Speed
• Acceleration

Answer: Speed

Speed is a scalar quantity, while displacement, velocity, and acceleration are vector quantities.

• 15 km/h
• 30 km/h
• 60 km/h
• 20 km/h