Forces and motion

• Newton's first law- If the resultant force acting on a stationary object is zero, then the object will remain stationary. If the resultant force acting on a moving object is zero, then the object will continue moving in the same direction and velocity.
• A resultant force causes an objects speed to change. It is the overall force acting on an object.
• Newtons Second Law- The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass.
• Force (N)= Mass (kg) x Acceleration (m/s2)
• The inertial mass is a measure of how difficult it is to change the velocity of an object.
• Newtons Third Law- When two objects interact, the forces they exert on each other are equal and opposite.
• Velocity is a vector quantity as it includes both magnitude and direction.
• The acceleration of an object tells us the change in its velocity over a given time.
• Acceleration (m/s2) = change in velocity (m/s) / time (s)
• The gradient of a velocity time graph tells us the acceleration of an object
• The total area under a graph tells us the distance travelled in a specific direction.
• Terminal velocity is the speed when an object falling through a fluid (usually air) is no longer getting faster. Terminal velocity happens at the moment in time that the force of gravity, called weight, is the same as the opposite force of air resistance or friction.
• Inelastic deformation- overstretching a spring so that the graph exceeds the limit of proportionality.
• Elastic materials will always return to their original length or shape if we take away the forces acting upon them.
• Force (N)= Spring Constant (N/m) x extension (m)
• Work- Whenever a force is used to move an object, energy is transferred
• Work done (J)= Force (N) x Distance (m)
• Firstly, when the skydiver jumps out they experience a resultant force acting downwards because of weight. They begin to accelerate and air resistance acts upwards. At a certain point the air resistance balances weight and there is no resultant force so the velocity is constant. Terminal velocity.
• Next, the skydiver opens their parachute which increases the surface area and causes air resistance to increase. A resultant force acts upwards which causes the skydiver to decelerate. Because the velocity decreases the air resistance decreases. They reach terminal velocity again and land.
• When a spring stretches it stores elastic potential energy. When it returns to its unstretched position this energy is released as kinetic energy. The total amount of energy stays the same throughout the process.
• The stopping distance is the total distance travelled from when the driver first spots the obstruction to when the car stops
• The thinking distance is the distance travelled by the car during the drivers reaction time.
• The braking distance is from when the driver applies the breaks to when the car stops.
• The overall stopping distance = Thinking Distance + Braking Distance
• Alcohol, drugs, distractions, driving too close to vehicles and tiredness can increase thinking distance.
• Wet or icy conditions and worn tires and brakes reduce the friction between the tyres and road and increase the braking distance.
• When driving at night it's important that your headlights are working properly as they will allow you to see further ahead which reduces the thinking distance.
• Weight is a measure of the force of gravity acting on an object. Measured in newtons.
• Weight= mass x gravitational field strength ( on the earths surface this is 10N/kg)
• The extension of a material is directly proportional to force
• Energy stored in a stretched spring= area under graph
• Car safety features include: seat belts, air bags and crumple zones. They reduce the force on a passenger during a crash by increasing the distance over which work is done to bring the vehicle to a stop.
• V= U + at
• x= ut + 1/2 at2
• x= (u+v)/2 x t
• Mass is an expression of the inertia of a body
• An object will remain at rest or in uniform motion in a straight line unless acted upon by an external resultant force.
• You can improve energy efficiency of vehicles by reducing aerodynamic losses, air resistance and rolling resistance, idling losses and inertial losses
• Aerodynamic losses are reduced by more streamlined designs. Rolling resistance is reduced by having correctly inflated tyres and using materials which don’t heat up as much as they are squashed. Stop – start systems reduce idling losses. Inertial losses are reduced by having lighter cars.
• Car safety features cause the same change in momentum to happen over a longer time so there is decreased deceleration so the force decreases.