Forces Flashcards
what are scalars and vectors?
- scalars have magnitude only
- vectors have a magnitude and a given direction
how can vectors be represented?
with an arrow
- length of arrow= size of vector
- direction of arrow=direction of vector
what are contact and non-contact forces?
- a push or pull that acts on an object due to the interaction with another object
- contact forces – objects are touching eg. friction, air resistance,
- non-contact forces – objects are separated eg. gravitational force, electrostatic force, magnetism
what is weight?
force of gravity acting on an object
weight equation
W=mg
what’s the centre of mass?
the single point where weight acts on an object
what is resultant force?
one force that has the same effect as all forces acting on an object
work done equation
W=Fs
what happens to an object temp is friction acts on it?
temp will rise as work is done against friction
force (elastic) equation
F=ke
what is the relationship between extension and force?
directly proportional until limit of proportionality isn’t exceeded
what is moment?
the turning effect of a force
moment equation
M=Fd
d is the perpendicular distance
what happens to the moments if an object is balanced?
total clockwise moment equals total anti-clockwise moment
what makes up a lever system?
- load
- effort
- pivot
how can a lever be used as a force multiplier?
distance between pivot and effort = greater than distance between pivot and load=force applied on load greater than effort force
what affects the moment of a gear?
its size
larger gear=slower+larger moment
what is a fluid?
a liquid or a gas
pressure equation
p=F/A
pressure on column of liquid equation
p=hpg
where do objects experience more pressure?
at the bottom of a column=resultant force up=upthrust
what influences whether an object floats or sinks?
- An object floats when its weight is equal to or less than the upthrust.
- An object sinks when its weight is greater than the upthrust
- The water level in a water container rises when an object is lowered into water given that the object displaces some water:
-the more the object is lowered into the water, the bigger volume that is displaced, causing a larger up thrust
-When an object is completely immersed in water, the weight of water displaced is equal to the force of up thrust acting on the object - A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface as pressure is proportional to the depth of the object
The difference in pressure creates a resultant force upwards (upthrust) - Upthrust is why objects appear to weigh less when immersed in a liquid
atmospheric pressure
- The atmosphere gets less dense as you go up
- Air molecules colliding with a surface create atmospheric pressure.
- atmospheric pressure decreases with an increase in height=less air above surface=less weight
what are the typical speeds for walking, running and cycling?
walking - 1.5 m/s
running - 3 m/s
cycling - 6 m/s.
car - 10-30 m/s
plane - 200-250 m/s
sound in air - 330 m/s
distance equation
s=vt
why does an object change its velocity when moving in a circle but go at the same speed?
- velocity is speed in a given direction
- if the direction of an object changes its velocity will change even if it goes at the same speed
acceleration equation
a=∆ v/t
uniform acceleration equation
v²-u²=2as
what is the acceleration of an object falling near earth’s surface?
9.8 m/s2 (falling freely under gravity)
what happens to an object falling through a fluid?
- initially accelerates due gravity
- eventually the resultant force will be zero = object will move at its terminal velocity
newton’s 1st law
- if an object is stationary or moving at a constant velocity, the object remains stationary or moving at a constant velocity unless an unbalanced force acts on it
what is inertia?
The tendency of objects to continue in their state of rest or of uniform motion
newton’s 2nd law
F=ma
newton’s 3rd law
for every reaction, there’s an equal and opposite reaction
what is stopping distance?
thinking distance (distance travelled in driver’s reaction time)+ braking distance (distance travelled until it brakes)
what is the average reaction time?
0.2-0.9s
what affects a driver’s reaction time?
- fatigue
- drugs
- alcohol
- distractions
what affects braking distance?
- adverse road+weather conditions eg. wet or icy
- poor vehicle conditions eg. tyres or brakes
what happens when a force is applied to brakes?
work done by friction between the brakes and the wheel=reduces Ek of the vehicle+temp of brakes increases
what happens to the deceleration of vehicle when it goes at high speed?
greater speed=greater braking force=greater deceleration
momentum equation
p=mv
what is the conservation of momentum?
In a closed system, the total momentum before an event is equal to the total momentum after the event eg collision or explosion
what is the difference between a collision and an explosion?
collision=go same direction
explosion=go different directions
conservation of momentum equation
m1v1+m2v2=mtotalvtotal
how does a change in momentum happen?
when force acts on an object that’s moving or can move
change in momentum equation
F =m∆v/t
rate of change in momentum
