FORCES

• Acceleration is a change in velocity
• The larger the change in force, the larger the momentum
• An elastic object is one that regains its shape when forces deforming it are removed
• factors affecting thinking distance: tiredness, alcohol, drugs, using phone
• factors affecting braking distance: poorly maintained roads, bad weather conditions, poorly maintained vehicles, load on car, speed
• The stiffer the spring, the greater its spring constant
• if a vehicle is travelling at steady speed, the driving forces are equal and opposite to the fricitional forces (air resistance and friction between tyres and road)
• the faster the speed of a vehicle, the bigger the deceleration needed to bring it to rest within particular distance
• a greater braking force is needed to produce a greater deceleration
• the greater the mass, the greater the braking force needed to produce a given deceleration
• crumple zones in cars are desgined to fold in collision and increase impact time reducing impact force
• helmets have crushable foam liner increasing impact time and reducing impact force
• playgrounds have cushionable surfaces increasing impact time and reducing impact force
• seatbelts and airbags spread impact force across large area
• airbags increase impact time on driver's head and chest and decreases impact force
• side impact bars fold up in a collision increasing impact time and reduces impact force
• Inertia is the tendency of an object to remain in its state of rest or moving at same velocity
• inertial mass of an object is measure of difficulty of changing the object's veolcity
• hooke's law is expressed as F=ke
• the greater the mass and velocity of an object, the greater its momentum
• if the velocity of an object changes, it must be acted on by a resultant force and its acceleration is in same direction as resultant force
• the velocity of an object increases if the resultant force is in same direction as velocity
• the velocity of object decreases if resultant force is in opposite direction as velocity
• if a vehicle is travelling at steady speed, resultant force on it is 0 as driving forces are equal and opposite to the frictional forces which are air resistance and friction between tyres and road
• the faster the speed of a vehicle, the bigger the deceleration needed to bring it to rest within particular distance
• greater breaking force is needed to produce a greater deceleration
• greater the mass the greater the braking force needed to produce a given deceleration
• NEWTONS SECOND LAW OF MOTION: acceleration of object is proportional to resultant force on object and inversely proportional to mass on object
• LAW OF CONVERSATION OF MOMENTUM states that total momentum before=total momentum after
• gears multiply effect of turning force using moments
• gears consist of wheels with toothed edges that fit together into teeth of each other where one rotates clockwise and the other anticlockwise
• if larger gear is driven by smaller one, the larger will rotate slower than smaller but will have greater moment. A low gear gives low speed and high turning effect
• if smaller gear is driven by larger one, the smaller will rotate quicker but have smaller moment.
• a moment is the turning effect of a force about a pivot
• You can increase the size of moment by: increasing magnitude of force, increasing perpendicular distance from line of force to pivot
• PRINCIPLE OF MOMENTS STATES: when object is in rotational equilibrium, the sum of clockwise moments is equal to anticlockwise moments about any point
• NEWTONS THIRD LAW OF MOTION states whenever two bodies interact, the forces they exert on each other are equal and opposite
• Resultant force is single force that describes all the forces operating on a body. When many forces are applied to an object, they can be combined to produce a single force
• NEWTONS FIRST LAW OF MOTION states that objects will remain at rest or constant velocity unless acted upon so resultant force is 0
• balanced forces means that the forces have combined in a way to cancel each other out and no resultant force acts on the body