Forces and Energy Flashcards
SI unit of force
Newton (N)
definition of a force
push or pull that
changes shape/size of obj.
moves/stops obj.
changes direction of moving obj.
slows down/speeds up moving obj.
what is used to measure force
force-meters
Newton meters (e.g. spring balance)
what is a contact force
forces acted between 2 objects physically touching
what is a non-contact force
forces acted between 2 objects not physically touching
5 contact forces
resistance
spring force
tension
applied force
normal contact force
3 non-contact forces
gravitational force
magnetic force
electrostatic force
what is normal contact force
force exerted on object due to its contact with another object
what is a gravitational field
region which a mass experiences a force due to gravitational attraction
what is a gravitational field strength
gravitational force acting per unit mass
formula of weight
W = mg (m = mass, g = gravitational field strength)
SI unit for weight
Newton (N)
what is friction
contact force that opposes motion or tendency for motion
why is there friction
microscopically, surfaces/objects are rough jagged
as 2 surfaces slide against each other, they grind and drag to create friction
3 benefits of friction
graphite pencil marks a mark on paper due to friction
warms hand when rubbed
friction between wheels and brakes slows down bicycles
3 downsides of friction
wears out rubber tyres
engines/axels may lose energy due to friction
air resistance slows down car
3 ways to reduce friction
lubricants
streamlined body to reduce air/water resistance
wheels/rollers/ball bearings (circular shape reduces C.S.A)
what is resultant force
single force that has same effect as 2 or more forces acting together
what is pressure
ratio of magnitude of force applied to area on which it is applied
SI unit of pressure
Pascal (Pa) or N/m²
formula of pressure
F (N)/A (m²)
what is atmospheric pressure
pressure exerted by air in Earth’s atmosphere
what is moment of a force
turning effect produced by force
formula of moment of force
Moment of force = force (N) x perpendicular distance from pivot (m)
SI unit of moment of force
Newton-metre (Nm)
what is a pivot/fulcrum
point about which a force turns
what does the Principle of Moments state
when obj. is in equilibrium
sum of clockwise moments about any point
is equal to sum of anti-clockwise moments about the same point
what is energy
ability to do work
SI unit of energy
Joule (J)
what is potential energy
energy stored in a body due to its condition/position
what is energy in action
energy that is in motion in a medium that has the ability to do work
what is GPE
energy a body possesses due to its position relative to the ground
3 points
what does GPE depend on
mass (m) of obj.
height (h) obj. is at
gravitational field strength (g) obj.is in
what is EPE
energy stored in elastic obj. when push or pulled
what is CPE
energy which holds the atoms and molecules of a substance together
this stored energy is released during chemical reactions
what is NE
energy in the nucleus of an atom which holds protons and neutrons together
this energy is released during nuclear reactions
what is nuclear fission
breaking down of a larger nucleus
by bombarding atom of a fuel with a neutron
splitting it into 2 smaller nuclei
and 2 or 3 neutrons to carry on reaction with another 2 or 3 fuel atoms
(used in nuclear bombs and nuclear power stations)
what is nuclear fusion
fusing of 2 small nuclei
to form 1 larger, unstable nucleus
giving off energy in the form of a fast-moving neutron
(found in hydrogen bombs and stars)
difference between CPE and NE
CPE: energy released when there is forming of bonds between atoms and molecules
NE: energy released when there is change in atomic structure of an element
what is KE
energy a body possesses due to its motion
what does KE depend on
mass (m) of obj.
speed (v) of obj.
what is LE
energy which enables us to see and do work
what is TE
energy which flows from a region of higher temperature to a region of lower temperature
what is EE
energy made available by the flow of electric charges such as electrons and ions (most useful form of energy as it can convert to other forms easily)
what is SE
energy produced by vibrations which can be detected by our ears
3 points
what does the Principle of Conservation of Energy state
energy cannot be created nor destroyed
can be converted from 1 state to another/transferred from 1 body to another
total amount of energy will be same before and after change or transfer
3 ways to save energy
take public transport
switch off appliances when not in use
use fans instead of air-conditioners
SI unit of work
Joule (J)
2 points
what conditions need to be met for work to be done
force acts on object
object moves in same direction as force
formula of work
W = F x d (F = force, d = distance moved by obj. in direction of force)
