Newton's First Law
- The resultant force can either be positive for negative.
5N←o→7N (7+5 = 12N) 12N
5N←O→7N (7-5 = 2N) 2N
- Resultant force = 0 → no change in velocity (direction & magnitude).
- Resultant force = not 0 → change in velocity (direction & magnitude).
- Momentum is the product of an objects mass & velocity.
- Momentum = mass x velocity
- kgms-1 = kg x m/s
- p = m x v
- Inertia is the reluctance to change:
-stationary → to move
-moving → change velocity
- Mass is the measure of an objects inertia.
- Momentum is the expression of a moving objects ineria.
- Greater mass = greater inertia
- Greater momentum = greater inertia
Newton's Second Law
- Acceleration is proportional to the force (constant mass).
- Acceleration is inversly propotraional to the mass.
Force = mass x acceleration
Resultant force = mass x acceleration
Resultant force = change in momentum/time
- Weight is a result of gravity fom a planet pulling on an objects mass.
- On Earth - every kg of mass experiences a graviational pull of 9.81N.
Weight = mass x gravity
W = m x g
- Gravity depends on the mass of the planet (proportional).
- The further the object is from the centre of the planet (core), the smaller the gravitational pull is.
- Resistance is friction.
- Resistance increase with speed (speed x2 = friction x4).
- As the speed of a falling object increase = air resistance increases
-resistance & friction act opposite to movement
-resistance increases as speed2 increases
-greater surface area = greater friction / air resistance
-fluid resistance (air / liquid) depends on collision of paricles with moving object
-denser fluid = greater resistance (more paricles per volume).
Falling Vertically (1)
- Resultant force = weight - air resistance
-air resistance increases
-weight stays the same
1. At start - not moving
- air resistance = 0
- resultant force = max.
- acceleration = max.
2. Moving / Falling / Speeding up
- air resistance = increases
- resultant force = decreases
- acceleration = decreases
- weight = unchanged
Falling Vertically (2)
3. Resultant is 0
- air resistance increase until it = to weight
- acceleration = 0
- weight = air resistance } terminal velocity
- velocity = constant } terminal velociy
4. Parachute opens
- air resistance = increases / greater than weight
- resultant force = negative → upwards
- surface area = increases
- deccelerating force - acceleration = negative → slows down
- air resistance = max.
- resultant force = max. negative value
Falling Vertically (3)
5. Slowing down
- air resistance = decreases
- resultant force = less negative (increasing)
- acceleration = less negative (increasing)
- weight = stays the same
reaction force ↑
air resistance / drag →
-drive - drag
-mass x acceleration
-positive → accelerating
-0 → velocity constant
-negative → deccelerating
Velocity & particle collision
As velocity increases:
- collisions with air resistance increases
- there is a greater rate of collisions
- there is greater momentum
- there is greater air resistance
Falling with negligible air resistance
- The moon has no air resistance.
- A brick is a dense object.
- In the absense of air resistance, all objects fall with at the same rate.
- Acceleration is due to gravity (9.81 m/s/s).