P5 - Forces and Motion - End of Topic - Part 2
L17 and L18 - Newton's Laws of Motion
Newtons 1st Law states that when an object has a resultant force of 0N, it will either remain stationary (provided it is already stationary), or it will continue to move at the same, constant velocity.
L16 - Velocity and Acceleration
Acceleration = (Final Velocity - Initial Velocity / Time)
a = (v - u / t)
Metres/Second^2 = (m/s - m/s / s)
Deceleration is an an acceleration in the other direction (negative acceleration).
Method:
- Set up air track and light gates; the gates should be fairly far apart and should be connected to a data logger (the logger should calculate acceleration)
- - Fix a piece of string onto a pulley, on one side of the string, a mass carrier should be present. The other side of the string should be connected to the trolley.
- - The trolley should be able to pass through the second gate before the masses hit the floor.
- - Steady the trolley, add the maximum weight increment and release the trolley; record the acceleration as stated by the logger.
- - When removing weight from the mass carrier, the removed weights must be placed back on the trolley to ensure the total mass of the system remains the same.
100g ~= 1N of Weight
Newton's 2nd Law states that an objects acceleration is proportional to the resultant force acting on it and inversely proportional to the objects mass.
Newton's 3rd Law states that when two objects exert a force on eachother; the forces are equal in magnitude and type but opposite in direction.
The tendency of objects to remain in rest or uniform motion is known as inertia.
L19 - Stopping Distances
Stopping distance is a sum of the thinking distance and the braking distance.
As speed increases, both braking and thinking distance increases.
Factors that can affect stopping distance:
- Drinking and using drugs can increase reaction times (thinking)
- - Weariness (thinking)
- - Mobile phones/distractions (thinking)
- - Weather conditions; icy road (braking)
- - Poorly maintained vehicles and brakes (braking)
L20 - Momentum
Momentum = Mass x Velocity
p = m x v
kgm/s = kg x m/s
The more momentum something has, the more force it requires to stop.
Some vehicles possess such features as crumple zones, seat belts and air bags. These features increase the amount of time of a collision, therefore decreasing the force (momentum is constant).
Force = Momentum / Collision Time
F = p / t
Newtons = kgm/s / s
L22 - Terminal Velocity
- When a skydiver initially jumps from a plane, the only force acting on him is weight (caused by acceleration due to gravity). He will accelerate at a constant rate.
- - As the diver gets faster, the air resistance (drag) acting on him will increase(increase in acceleration in the negative direction). This will continue to occur until the drag acting on the diver is equal to his weight.
- - This resultant force of 0N means that the diver will be travelling at a constant velocity and will have no acceleration.
- - This state can only be exited if the diver is to physically change something. Deploying a parachute increases the drag force massively; creating a resultant force in the up direction. The diver decelerates. This diver will still be falling, however.
Terminal velocity occurs when the resultant force on a body is 0N.
L23 - v^2 = u^2 + 2as
v^2 = u^2 + 2as
Final velocity^2 = Initial velocity^2 + (2 x Acceleration x Displacement)
(Metres/Second)^2 = (Metres/Second)^2 + (2 x Metres/Second^2 x Metres)