EJC Physics H202 Kinematics 2023_1. Notes (FULL)

Content • Rectilinear motion • Non-linear motion Learning Outcomes Candidates should be able to: (a) show an understanding of and use the terms distance, displacement, speed, velocity and acceleration (b) use graphical methods to represent distance, displacement, speed, velocity and acceleration (c) identify and use the physical quantities from the gradients of displacement-time graphs and areas under and gradients of velocity-time graphs, including cases of non-uniform acceleration (d) derive, from the definitions of velocity and acceleration, equations which represent uniformly accelera ted motion in a straight line (e) solve problems using equations which represent uniformly accelerated motion in a straight line, including the motion of bodies falling in a uniform gravitational field without air resistance (f) describe qualitatively the motion of bodies falling in a uniform gravitational field with air resistance (g) describe and explain motion due to a uniform velocity in one direction and a uniform acceleration in a perpendicular direction. Kinematics describe the motion of points, bodies and systems of bodies without considering the forces that cause them to move. Before we can fully appreciate the motion, we need a common vocabulary to help establish an understanding of the science behind describing motion. Kinematics is often referred to as the “geometry of motion” as the values of position, displacement, velocity and acceleration are worked on mathematically without considering the type of force causing the motion. We shall talk about how forces act on bodies in the topic of Dynamics. “Perseverance” Mars rover landing. The intense entry, descent, and landing (EDL) phase begins when the spacecraft reaches the top of the Martian atmosphere, traveling at nearly 20 000 kmph. Many refer to the time it takes to land on Mars as the “seven minutes of terror.”

We typically denote position vectors using s with respect to an origin. Then the displacement (or change in displacement) can be final initials s s = − . Example 1 A car travels on a straight horizontal road. It starts moving at time t = t1 and comes to a stop momentarily at t = t2. It then reverses and comes to a stop again at t = t3. Taking rightwards direction as positive, state the (a) total distance travelled, and (b) displacement of the car with respect to origin x = 0. –30 –20 –10 0 10 20 30 40 x/m distance / m t = t1 t = t2 t = t3 time distance travelled displacement from origin t1 0 m 0 m t2 30 m +30 m or 30 m to the right t3 90 m –30 m or 30 m to the left y x Note: It is quite conventional to take rightwards as positive for horizontal motion and upwards as positive for vertical motion. It is equally conventional to take the direction normal and away from an inclined surface as positive displacement from the su