Speed and Distance
- To find the speed of an object, you need to measure the distance it travels (in metres or km) and the time it takes (in seconds or hours) Then the speed is calculated in metres per second (m/s) or kilometres per hour (km/h)
- Speed, distance and time are related by the formula: Distance = Speed * Time
- If an object is speeding up or slowing down then you might need to find the average speed over the journey: Average Speed = (u+v)/2
- U is the speed at the start and V is the speed at the end
- Distance = Average Speed * Time = (u+v) / 2 * t
- Important Notes:
Gradient = Speed
Flat sections are where it's stopped
The steeper the gradient, the faster it's going.
Downhill sections (negative gradient) mean it's changed direction and it's coming back towards its starting points
Curves represent acceleration or deacceleration
A steepening curve means it's speeding up (increasing gradient)
A levelling off curve means its slowing down (decreasing gradient)
- Calculating Speed from a Distance - Time Graph: Speed = Gradient = vertical / horizontal = 500/30 = 16.7 m/s
Speed and Acceleration
- Acceleration is how quickly the speed is changing.
- You can also accelerate when you change direction, with or without changing speed/
- Units: m/s^2
- Acceleration = Change in speed / time taken or Change in speed / a * t
Gradient = Acceleration
Flat Sections represent steady speed
Steeper the gradient, The greater the acceleration or deceleration
Uphill +ve gradients are acceleration
Downhill -ve gradients are deceleration
The area under any section of the graph is the distance travelled in that time interval.
A curve means non-uniform (changing) acceleration or deceleration.
- Calculating Acceleration, Speed and Distance from a Speed-Time Graph : gradient = vertical / horizontal = 30 / 20 = 1.5 m/s^2
- The speed of an object is just how fast it's going - the direction isn't important
- Velocity describes both the speed and direction of an object E.g. velocity = 30mph due north
- If the object turns in the opposite direction, the velocity is negative
- If two objects are moving parallel to each other, the relaticve velocity is the difference in their velocities.
Mass, Weight and Gravity
- Gravity is the force of attraction between all masses.
- Gravity makes all things accelerate towards the ground, all with the same acceleration
- G is the acceleration due to gravity and it's also known as the gravitational field strength. The value of g is about 10 m/s^2 on Earth. It's different on other planets and can vary slightly in different places on Earth.