forces, acceleration and newton's law
Terminal velocity
At terminal velocity, the object moves at a steady speed in a constant direction because the resultant force acting on it is zero.
For example, a skydiver falling spread-eagled through the air reaches a maximum speed of about 53 m/s.
the stages of an object falling through a fuild
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at the start, the object accelerates downwards
due to the force of gravity
as the object's speed increases, frictional forces such as
air resistance or drag increase
at terminal velocity, the weight of the object due to gravity is balanced by the frictional forces, and the resultant force is zero
The weight of an object does not change as it falls, as long as it stays whole.
Newton's First Law
Newton's First Law of motion, an object remains in the same state of motion unless a resultant force acts on it. If the resultant force on an object is zero,
a stationary object stays stationary
a moving object continues to move at the same velocity (at the same speed and in the same direction)
Inertia
The tendency of an object to continue in its current state (at rest or in uniform motion) is called inertia.
Newton's First Law can be used to explain the movement of objects travelling with uniform motion (constant velocity).
Newton's First Law can also be used to explain the movement of objects travelling with non-uniform motion.
For example, when a car travels at a constant speed, the driving force from the engine is balanced by resistive forces such as air resistance and friction in the car's moving parts. The resultant force on the car is zero.
This includes situations when the speed, the direction, or both change. For example, when a car accelerates, the driving force from the engine is greater than the resistive forces. The resultant force is not zero.
Newton's second law
Newton's Second Law of motion can be described by this equation:
resultant force = mass × acceleration
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force (F) is measured in newtons (N)
mass (m) is measured in kilograms (kg)
acceleration (a) is measured in metres per second squared (m/s²)
The equation shows that the acceleration of an object is:
proportional to the resultant force on the object
inversely proportional to the mass of the object
Inertial mass - Higher
The ratio of force over acceleration is called inertial mass. Inertial mass is a measure of how difficult it is to change the velocity of an object.
newton's Third law
whenever two objects interact, they exert equal and opposite forces on each other.
This is often worded as 'every action has an equal and opposite reaction'. However, it is important to remember that the forces act on two different objects at the same time.
forces and braking
stopping distances
In an emergency, a driver must bring their vehicle to a stop in the shortest distance possible:
stopping distance = thinking distance + braking distance
thinking distance is the distance a vehicle travels in the time it takes for the driver to apply the brakes after realising they need to stop
braking distance is the distance a vehicle travels in the time after the driver has applied the brake