Forces and Motion

Contents Velocity and Acceleration Velocity and Acceleration D-T Graph D-T Graph S-T Graph S-T Graph Newton’s Laws of Motion Newton’s Laws of Motion Forces and Acceleration Forces and Acceleration

Velocity and Acceleration Speed = how fast something travels Speed = how fast something travels Velocity = how fast something travels in a direction Velocity = how fast something travels in a direction Acceleration = change in speed in a given time Acceleration = change in speed in a given time v = final velocity, u = initial velocity v = final velocity, u = initial velocity d st v-u at

D-T Graph Distance (m) Time (secs) Steady speed Stopped Accelerating Decelerating

S-T Graph Speed (m/s) Time (secs) Acceleration Steady speed Increased acceleration Decreased acceleration Deceleration

Newton’s Laws of Motion 1 st Law: Balanced forces = constant velocity 1 st Law: Balanced forces = constant velocity Steady Forces: Steady Forces: - Vertical (e.g. parachutist at terminal velocity) weight force = drag force - Horizontal (e.g. car moving at steady speed) thrust force = drag force 2 nd Law: Resultant force = acceleration in that direction 2 nd Law: Resultant force = acceleration in that direction Acceleration: starting, stopping, speeding up, slowing down, changing direction Acceleration: starting, stopping, speeding up, slowing down, changing direction

Newton’s Laws of Motion 3 rd Law: every action has an equal and opposite reaction 3 rd Law: every action has an equal and opposite reaction E.g. a book on a table E.g. a book on a table The book’s weight (mass x gravity) pushes down on the table The book’s weight (mass x gravity) pushes down on the table The table pushes back with a reaction force The table pushes back with a reaction force Size of action (weight) = size of reaction Gravity on Earth, g = 10m/s 2 Gravity acts towards the centre of the Earth

Forces and Acceleration Resultant Force = overall unbalanced force Resultant Force = overall unbalanced force Any resultant force produces acceleration Any resultant force produces acceleration F = force (N) m = mass (kg) a = acceleration (m/s 2 ) F ma

1) A car travels at a steady speed… the thrust force is equal to the drag force. This does not necessarily mean that the car is stationary, but it does mean that the car is neither accelerating nor decelerating. 2) A car accelerates from rest. The forward arrow (thrust) is larger than the backward arrow (drag). The car will accelerate in the direction of the bigger arrow

Summary distance (m) = speed (m/s) x time (s) distance (m) = speed (m/s) x time (s) Velocity is speed with a direction e.g. 10m/s Northwards Velocity is speed with a direction e.g. 10m/s Northwards Acceleration (m/s 2 ) = change in speed (m/s) / time taken (s) Acceleration (m/s 2 ) = change in speed (m/s) / time taken (s) a = (v-u)/t a = (v-u)/t Balanced forces = constant velocity (this can be stationary) Balanced forces = constant velocity (this can be stationary) Unbalanced forces (resultant) = change in velocity (+ve / –ve) Unbalanced forces (resultant) = change in velocity (+ve / –ve) Every action force has an equal and opposite reaction force Every action force has an equal and opposite reaction force Force (N) = mass (kg) x acceleration (m/s 2 ) Force (N) = mass (kg) x acceleration (m/s 2 ) The difference between opposite forces = resultant force. An object will accelerate / decelerate according to its size The difference between opposite forces = resultant force. An object will accelerate / decelerate according to its size