Forces and Motion

• Speed and velocity are both how fast you are going
• Speed and velocity are both measured in metres per second (m/s) or metres per hour (or km/h or mph)
• Speed is how fast you are going with no regard to the direction.
• Velocity however is the speed of an object in a given direction.
• You can have objects travelling at a constant speed with a changing velocity. This happens when the object is changing direction while staying at the same speed.
• average speed = distance / time taken (m/s)
• Acceleration is how quickly the velocity is changing
• Acceleration is not the same as velocity or speed. Acceleration is how quickly the velocity is changing.
• The unit of acceleration is m/s²
• acceleration = change in velocity / time taken
• distance time graphs tell you how far something has travelled
• The different parts of a distance time graph, describe the motion of an object
• Distance time graphs: The gradient at any point gives the speed of the object
• Distance time graphs :Flat sections are where it’s stopped
• Distance time graphs: A steeper graph means it’s going faster
• Distance time graphs: curves represent acceleration
• Distance time graphs: a curve getting steeper means it’s speeding up
• Distance time graphs: a level of curve means it’s slowing down
• Distance time graph:

  
• You can calculate the average speed of an object over a period of time, by dividing the total distance, travelled by the time it takes to travel that distance.
• Velocity time graphs can have a positive or negative gradient.
• How an object velocity changes overtime can be plotted on a velocity time graph.
• Velocity time graph: gradient = acceleration
• Velocity time graph: flat sections represent steady speed
• Velocity time graph: the steeper, the graph, the greater, the acceleration or deceleration
• Velocity time graph: uphill sections are acceleration
• Velocity time graph: downhill sections are deceleration
• Velocity time graph: the area under any part of the graph is equal to the distance, travelled in that time interval
• Velocity time graph: a curve means changing acceleration
• Velocity time graph:

  
• Gravity is the force of attraction between all masses
• Gravity attracts all masses, but you only notice it when one of the masses is really really big e.g a planet. Anything near a planet or star is attracted to it very strongly.
• Gravity: On the surface of a planet, it makes all things accelerate towards the ground.
• Gravity: it gives everything a weight
• Gravity: it keeps planets, moons and satellites in their orbits.
• Weight and mass are not the same
• Mass is just the amount of ”stuff” in an object.
• Weight is caused by the pull of gravity. In most questions, the weight of an object is just the force of the gravity pulling it towards the centre of the Earth.
• An object has the same mass, whether it’s on earth or on the moon, but it’s weight will be different.
• Weight is a force measured in newtons.