Forces Flashcards
What is the differecne between distance and displacement?
Distance
how far an object travels
scalar quanitity (no direction)
Displacement
the total straight distance from the starting to ending point
vector quantity (includes direction)
What is the light gate equation?
The speed of an object when it travels through a light gate is
v = x / t
Where x is the length of the card, V is the speed and t is the time taken.
What are the four acceleration formulae?
1) acceleration = change in velocity / time
2) final speed² - inital speed² = (2 x acceleration) x distance
3) final speed = inital speed + (acceleration x time)
4) Force = mass x accelleration
What is the percentage change formula?
(fin - in)/in x 100
What is newton’s first law?
An object will remain at stationary or moving at a constant velocity unless acted upon by a resultant force.
What is Newton’s second law?
The acceleration of an object is directly proportinal to to the resultant force applied, and inversely proportional to it’s mass.
F = ma
(where f is the resultant force, m is the mass, and a is the acceleration)
What is Newton’s Third Law?
Every action has an opposite and equal reaction.
How do we calculate momentum?
(and units!)
p = mv
momentum (kgm/s) = mass (kg) x velocity (m/s)
What is conservation of momentum?
the sum of momentum BEFORE collision = the sum of momentum AFTER collision
momentum cannot be created or destroyed.
How do we calculate a change in momentum?
Δp = mv - mu
change in momentum = (final velocity x mass) - (initial velocity x mass)
How do we calculate force from momentum?
Force = change in momentum / change in time
What safety features are built into cars and what purpouse do they serve in preventing injury?
Air bags, crumple zones, seat belts.
- They absorb the kinetic energy transferred by collisions
- They increace the time taken for the change in momentum to happen, and therefore reduces the forces involved.
Using ideas about momentum, describe how a rocket is launched.
The rocket starts at rest and has no momentum.
The rocket pushes the fuel out of the bottom of the rocket. The fuel has gained momentum in the direction of the ground (earth).
The conservation of momentum means that the rest of the rocket must gain momentum in the opposite direction. This propels (pushes) the rocket into the sky.
What is mass?
The amount of matter the object contains. This is constant and remains the same regardless of gravitational field strength.
Density / Volume
What is inertia?
An object’s tendency to remain stationary or in uniform motion.
The greater an object’s mass, the greater its inertia. The smaller an object’s mass the smaller it’s inertia.
What is equation for weight
W = mg
Weight (N) = mass (kg) x gravitational field strength. (N/kg)
Provide two apparaus that are used to measure WEIGHT
- Calibrated spring scale
- Top pan digital balance
What is the acceleration of an object in free fall?
9.81 m/s² (often rounded to 10m/s²)
(accelerating at a constant rate due to gravity/weight)
What is the centripital force?
When an object is in cirular motion, there is a resultant force acting in the centre of the circle, therefore the object is accelerating towards the centre.
What is an interaction pair?
a set of 2 forces that are equal and opposite, acting on 2 interacting objects.
What is centre of mass?
The point through which an objects weight appears to act
Why does an object fall over?
Because it’s centre of mass is outside it’s perimiter
Why shouldn’t lots of people stand on the top deck of a bus?
(2 marks)
More people on the top deck of buses means the centre of mass will be higher.
Therefore, a smaller tilt of the bus is required to place the bus’ centre of mass outside of its wheels, causing the bus to tip.
(2 marks)
What is resultant force?
The sum of all the forces acting on an object
What was Hooke’s Law?
The extention of an elastic object is directly proportional to the force applied to it
in other words, force = spring contstant x extention
(the higher the spring constant, the stiffer the spring.)
What is the limit of proportionality?
When an elastic object is stretched too much, it becomes inelastically deformed and cannot return to it’s original form.
What is the formula for the elastic potential energy stored in a spring?
Elastic potential energy = 1/2 x the spring constant x extention²
What does the area under a force extention graph show?
The total elastic potential energy
What is a moment?
A moment is the turning effect of a force around a fixed point.
How do we calculate a moment?
moment = force × (perpendicular) distance (from the pivot)
Recite the pressure formula
pressure (Pa) = force (n) / area
