forces

• when the resultant force on an object is zero, it is in equilibrium and does not move, or remains at a constant speed in a straight line.
• one effect of a force is to change an objects form, causing it to be stretched or compressed. in some materials, the change is proportional to the force applied.
• equilibrium - state of an object when opposing forces are balanced.
• deformation - changing shape due to a force.
• linear relationship - when two variables are graphed and show a straight line which goes through the origin, and they can be called directly proportional
• Newton - unit for measuring forces
• resultant force - single force which can replace all the forces acting on an object and have the same efeect.
• friction - force opposing motion which is caused by the interaction of surfaces moving over one another. it is aclled drag if one is fluid
• tension - force extending or pulling apart
• compression - force squashing or pushing together
• contact force - one that acts by direct contact
• pressure acts in a fluid in all directions. it increases with depth due to the increase weight of fluid, and results in an upthrust. objects sink or float depending on whether the weight of the object is bigger or smaller than the upthrust.
• different stresses on a solid object can be used to explain observation where objects scratch, sink into or break surfaces
• fluid pressure, or stress on a surface = force (N)/area(m2)
• fluid - a substance with no fixed shape, a gas or a liquid
• pressure - the ratio of force to surface area, in N/m^2, and how it causes stresses in solids
• upthrust - the upward force that a liquid or ags exerts on a body floating in it
• atmospheric pressure - the pressure caused by the weight of the air above a surface
• mass and weight are different but related. mass is a property of the object; weight depends upon mass but also on gravitational field strength
• every object exerts a gravitational force on every other object. the force increases with mass and decreases with distance. gravity holds planets and moons in orbit around larger bodies
• weight(N)=mass(kg) x gravitational field strength(N/kg)
• g on earth = 10N/kg. on the moon it is 1.6N/kg
• weight - the force of gravity on an object
• non contact force - one that acts without direct contact
• mass - the ammount of stuff in an object
• gravatational field strength - the force from gravity on 1 kg (N/kg)
• field - the area where other objects feel a gravatational force
• if the overall, resultant force on an object is non zero, its motion changes and it slows down, speeds up or changes direction
• speed=distance (m)/time(s)
• a straight line on a distance time graph shows constant speed, a curving line shows acceleration
• the higher the speed of an object, the shorter the time taken for a journey
• speed - how much distance is covered in how much time
• average speed - the overall distance travelled divided by overall time for a journey
• relative motion - different observers judge speeds differently if they are in motion too, so an objects speed is relative to the observers speed