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forces (frictional forces: (to decrease friction, you can use a from of…
forces
frictional forces:
to decrease friction, you can use a from of lubrication.
By putting a layer of oil / liquid / air / gas between the surfeses, they will glide over one another more easily,
and it can also help cool them to
prevent loosing energy as heat.
roller bearings/ ball bearings can
also be used to reduse friction between
surfaces moving past each other / moving parts
different types of friction :
- air resistance
- water resistance
- ground friction
the size of friction depends on:
- the mass of the moving object
- the speed of the moving object
- the size of the contact area
more contact area = more friction
- the type of contact surface
rough surface = more friction
smooth surface = less friction
- friction arises whenever an object moves,
or tries to move over another object
- friction can cause loss of energy due to loosing energy as heat
- acts in opposite direction to the movement
- push force
- makes it harder to move
- acts whenever 2 surfaces are
in contact with each other
- drag opposing a push or thrust force
static vs dynamic friction:
static friction = if friction is able to prevent movement
dynamic friction = if friction is too small to prevent movement , then some kinetic energy is changed to heat energy in an effort to prevent movment
-
Newtons laws:
Inertia
Newtons 1st law:
balanced forces
An object at rest will remain at rest...
An object moving a constant velocity will continue to do so...
... unless acted upon by an unbalanced force
(if the forces are balances , objects move at a constant speed or are stationary)
Newtons 2nd law:
unbalanced forcesIf an unbalanced force acts upon an object the object will accelerate/decelerateThe acceleration is directly proportional to the force, and inversely proportional to the mass of the object:
- when the unbalanced forces are doubles, the acceleration doubles
- when the mass of the trolley is increases, then the acceleration of the trolley decreases
a = prportional = F(unb) / m
F(unb) = M x aa = acceleration (ms-2)
F(unb) = unbalanced force (N)
m= mass (kg)
Newtons 3rd law: For every action force there is an equal and opposite reaction forceaction & reaction forces always act in opposite directions, on opposite objectse.g.
- action force = the air pushed backwards
- reaction force = air pushes other air , pushing the balloon forward
terminal velocity/speed:
when forces acting on an object become balances, then the object moves with a constant velocity, this is called terminal velocity
constant velocity = terminal velocity
(the faster you move (more gravity) the more air resistance there is)
examples: (2x) A skydiver jumping out of a plane: 1) support from the plane + gravity = balanced forces, stationary 2) no support from the plane + gravity = unbalanced forces, accelerating down 3) air resistance increases because the speed has increased = no balanced forces, constant velocity down
(terminal velocity)4) parachute pulled, this increases the air resistance, so now there is less gravity = unbalanced forces and person accelerates up.5) because they've slowed down, the air resistance decreases and it is now balanced to the gravety = balanced forces, constant velocity down, but small than before (terminal velocity)when you pedal a bike harder, it accelerates. as the forward force is grater than the total froction force:
- as the speed becomes faster, air friction increases
- now that the total frinction force ncreases, it balances the push force. the bike moves at a constant velocity, called terminal velocity
Pressure:
the pressure of a force depends on the surface areas, over witch the force is spread
unit = Nm-2 ( newtons per square metre)
or Pa (pascels)
P = F/A
P = pressure (N/m) or (pa)
F = force (N)
A = surface area (m2)
larger surface areas = less pressure
smaller surface = more pressure
e.g. a blunt needle will have a bigger surface area, therefor you will need to aplly a greater force to achieve the same amount of pressure
what are forces:
- a push or a pull
- they act on other objects & each other
- vector quantities, (has both size and direction)
- when froces are equal they are called balanced froces
- there can be more than 1 force acting on an object at any one time
some examples of forces:
- Gravity force (Fg)
- friction force (Ff)
- Support force (Fsup.)
- Tension Force (Ft)
- weight force (Fw)
- thrust force (F thr.)
Drawing vector diagrams:Forces can be represented by drawing vectors, witch show direction and size (they are lines with arrows)
- the arrow points in the direction the force is acting
- vector lines must be rulled (straight)
- the size and direction of the vector lines shows the size and direction of the forces
- equally sized vectors show balanced forces
- there are horizontal & vertical forces / vectors
gravitational force:
- gravity is a non-contact force (it acts even when in a vacuum)
using a force-meter:
the number on the force-meter tells us how big the force is in newtons (N)
- forces are measured in newtons (N)