forces

• velocity and speed are not the same thing
• speed is a scalar quantity
• scalar quantities only have a magnitude, with no direction
• velocity describes an object's direction as well as its speed
• velocity is a vector quantity because it has a magnitude and a direction
• to add vectors, draw each vector as an arrow one after the other
• the length of the arrow on a vector represents the magnitude of a quantity
• the direction of the arrow on a vector represents the direction of the vector quantity
• acceleration = change in velocity / time taken
• distance is how far an object moves
• distance is a scalar quantity
• displacement is the distance an object moves in a straight line from a starting point to a finishing point
• displacement is a vector quantity
• a force is a push or a pull that acts on an object when it interacts with another object
• contact forces happen when 2 objects are physically touching
• friction, air resistance, tension and normal contact force are all examples of contact forces
• non-contact forces happen when objects are separated
• gravitational force, electrostatic force and magnetic force are all examples of non-contact forces
• friction comes about whenever 2 surfaces are touching and try to move against each other. tiny bumps in the surface interlock, creating a frictional force that opposes their motion
• air resistance comes about when an object moves through air and collides with air molecules, creating a force that slows the object down
• tension is the pulling force that a string or cable exerts when something or someone pulls it
• when you push a table, your hand doesn't move through it because the normal contact force from the table pushes equally on your hand
• the area under a velocity-time graph is equal to the distance travelled by an object
• to find the area under a velocity-time graph, break it down into small shapes and add the areas of the shapes
• area of triangle = 0.5 x base x height
• area of rectangle = base x height
• the mass of an object is a measure of the amount of matter it contains
• the mass of an object is constant as it is the same on earth, on the moon and in space
• an object's mass is also a measure of how difficult it is to change the object's motion, known inertia
• an object with a high mass has more inertia than an object with a lower mass
• it is difficult to move an object with a high mass, and once it is moving, the object's motion is hard to stop
• although the mass of an object is spread out across its body, it is possible to find a single point where all the mass appears to be, known as the object's centre of mass
• the centre of mass is the point through which an object's weight appears to act
• if an object is hung from a string, it will hang with its centre of mass directly below the point that it is hung from
• an object will fall over if its centre of mass is outside its base
• an object will fall off a surface if its centre of mass isn't over the surface
• a force may cause a mass to accelerate, which can be a change in speed, a change in direction or a change in both
• the resultant force is the sum of all of the forces acting on an object
• the change in an object's motion is caused by the resultant force
• if the forces acting on an object are unbalanced it means that a resultant force is acting on the object