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Forces and Motion

Forces and Motion. Contents. Velocity and Acceleration D-T Graph S-T Graph Newton’s Laws of Motion Forces and Acceleration. Velocity and Acceleration. Speed = how fast something travels Velocity = how fast something travels in a direction Acceleration = change in speed in a given time

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Forces and Motion

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  1. Forces and Motion

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

  3. Velocity and Acceleration • Speed = how fast something travels • Velocity = how fast something travels in a direction • Acceleration = change in speed in a given time v = final velocity, u = initial velocity d v-u s t a t

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

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

  6. Newton’s Laws of Motion • 1st Law: Balanced forces = constant velocity • 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 • 2nd Law: Resultant force = acceleration in that direction • Acceleration: starting, stopping, speeding up, slowing down, changing direction

  7. Newton’s Laws of Motion • 3rd Law: every action has an equal and opposite reaction • E.g. a book on a table • The book’s weight (mass x gravity) pushes down on the table • The table pushes back with a reaction force Size of action (weight) = size of reaction Gravity on Earth, g = 10m/s2 Gravity acts towards the centre of the Earth

  8. Forces and Acceleration • Resultant Force = overall unbalanced force • Any resultant force produces acceleration F = force (N) m = mass (kg) a = acceleration (m/s2) F m a

  9. 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

  10. Summary • distance (m) = speed (m/s) x time (s) • Velocity is speed with a direction e.g. 10m/s Northwards • Acceleration (m/s2) = change in speed (m/s) / time taken (s) • a = (v-u)/t • Balanced forces = constant velocity (this can be stationary) • Unbalanced forces (resultant) = change in velocity (+ve / –ve) • Every action force has an equal and opposite reaction force • Force (N) = mass (kg) x acceleration (m/s2) • The difference between opposite forces = resultant force. An object will accelerate / decelerate according to its size

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