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Physics {Forces, Acceleration & Graphs Summer} :revolving_hearts: -…
Physics {Forces, Acceleration & Graphs Summer} :revolving_hearts:
Units
second (s)- for time
m/s- for speed m/s^2- for acceleration
metre (m)- for distance
newton (N)- for force
kilogram (kg)- for mass :
N/kg- for gravitational field strength
Forces
change shape (stretch/deform)
change direction
change speed (accelerate/decelerate)
Formulas
acceleration= change in speed/time (a=(v-u)/t)
speed= distance/time (s=d/t)
weight= mass x gravitational field strength (w=mg)
force= mass x acceleration (f=ma)
final speed= initial speed + (2 x acceleration x distance) (v^2= u^2 + 2as)
average speed = total distance/total time
Vector vs Scalar Quantites
A vector quantity has a
magnitude and direction
.
Examples of scalar quantities:
speed, length, area, volume, power, energy, work, mass, density, temperature, pressure
A scalar quantity only has
magnitude
.
Examples of vector quantities:
velocity, force, weight
Friction
force that opposes motion
Exam Question
explain the acceleration of the aircraft
As the aircraft accelerates, the velocity increases which leads to a greater air resistance. The air resistance is an opposite force of the engine.The resultant force on the aircraft decreases as air resistance increases. Since the resultant force is reduced, the acceleration of the aircraft decreases.
Velocity Time Graph
The area under the line tells us the distance travelled.
If the line
inclines
, then the object is moving away from the starting point.
If the line
declines
, then the object is moving back to the starting point.
If the line is horizontal, the object is moving at a constant velocity.
Distance Time Graph
If the line is on a decline, the object is decelerating.
speed= rise/run
The horizontal line means the object is
stationary
.
The steeper the line the faster the speed.
If the line is on an incline, the object is accelerating.
Resultant Forces
if the resultant force is zero, the forces are balanced
if the resultant force is non-zero, then the forces are unbalanced
Stopping Distance
Thinking Distance-> reaction time from tired/intoxicated driver
Braking Distance-> mass, speed, road condition, tyre quality(friction)
Stopping Distance= Thinking Distance + Braking Distance
If the stopping distance increases, the driver will travel further in the same time.
Terminal Velocity
As object falls, the weight is the greater force so it accelerated downwards.
As the speed increases, the air resistance also increases.
When the air resistance is equal to the weight, the forces are balanced and the resultant force is 0.
This means the object is now travelling at a constant speed. This is known as terminal velocity.
If a skydiver opens their parachute, the air resistance increases so they would begin to decelerate.
Soon, the weight will equal the air resistance and now the skydiver will be travelling at a safer terminal velocity.
Gravitational
Field Strength
The Earth has a larger mass than the moon, so its gravitational field strength is greater.
Exam Question
explain why the feather reaches the ground after the hammer
Both objects are let go at the same time from the same height. They will both accelerate downwards with weight and the air resistance will increase as they go down. Since the hammer is heavier than the feather, its weight will be greater so the hammer spends more time accelerating than the feather because a large air resistance needs to be built-up to compensate. Therefore, the hammer has a higher terminal velocity (weight=air resistance) than the feather and reaches the ground first.
Glider Example
The cushion of air lifts the glider, this greater reduces air resistance (friction) as it moves. This allows the glider to move at a constant speed.