forces and energy (from notes) Flashcards
what is a force
push or pull
interaction
what can a force do
make a stationary object move
stop a moving object
make a moving object speed up or slow down
change the direction of a moving object
create a turning effect to make an object turn or rotate
change the shape or szie of an obj
what cant a force do
force cannot change the mass of an object (cannot take away or add matter)
SI unit for force
newton (N)
how can a force be measured
force meter/newton meter eg. spring balance
what is speed
measure of how fast an object moves, defined as the distance travelled per unit time. m/s or km/h
what will a larger force do (speed)
make object speed up more or slow down more
is force required if object is to move at constant speed?
no
what happens when an object’s mass increases? (speed)
force needed to change its speed increases
classify forces
contact
non-contact
contact force
force that acts between objects touching each other, eg friction
non-contact force
force that acts between objects that are not touching each other, eg. gravitational force, magnetic force
how to represent a force in drawing?
arrow
arrow indicates direction of force
length of arrow indifcates magnitude of force
how to describe a force?
naming force acting on object
by which other body
in a specific direction which is shown by the arrow
how to draw gravitational force?
from middle of object/center of gravity
how to draw friciton?
draw arrow on surface
what is grabitational force?
force that exists between objects that have mass
weight
amount of gravitational force acting on object, depends on both mass of object and garatiational force strength at location of object
formula of weight
W = mg
W - weight in N
m - mass in kg
g - gravitational field strength
what happens when you move much further away from Earths surface? (gravitational field strength)
gravitational field strength decreases
how to measure mass
electronic balance
beam balance
how to measure weight
extension spring balance
compression spreing balance
where to draw weight
centre of gravity
mass
amount of matter in object (number of particles)
SI unit for mass
kg
what does magnet exert
magnetic force. can be used to attract magnetic materials. can be used to attract or repel other magnets
friction
force that alwasys opposes motion of object (opposite direction)
when will object not move (friction)
when force applied is smaller than or equal to maximum friction possible
when does friciton act
when one surface rubs aainst other surface
air resisaance
fricitonal force experienced by moving object in air
when does friciton become greater
when surfaces are rougher
when object has a heavier weight
examples when friciton is useful
precents us from slipping when we wlak
it prevents ovnects form slipping from our hands
it allows us to light a matchstick
examples when friection can be a nuisance
when it causes surfaces to heat up
when it can wear down objects
when it can slow down movement
how to overcome friciton problems
apply lubricants between the surfaces
use of wheels and ball bearings
make surfaces smoother
streamlining
state of motion
describes how an object is moving
what happens if two or more forces act on an obj at the same time
resultant force is found by adding forces together, with both magnitude and direction considered
what happens when forces are balanced?
resultant force is zero. thus, objcet will continue to be at rest or move with a constant speed in a straight line
what happens whenforces are unbalanced
resultant force is not zero. (undergo acceleration (change in speed and/or direction of motion)
what does resultant force determine
final state of motion
What are some ways a resultant force can change the state of motion of an object?
start a body moving (speed increases from zero)
stop a moving body (speed decreases to zero)
change the speed of a body (speed increases or decreases)
change the direction of a moving body (speed remains unchanged/constant)
if an object moves at constant speed in one direction, what is the resultant force
0N
if an object moves against friction of 400N and it is at a constant speed, what is its driving force
400N
describe what happens to a stationary object on a floor when a pushing force acts on it, but pushing force is lower/equal than friction
- surface opposes motion of object. equal/less force of xN.
- resultant force =0???
- since object was initially at rest, it will remain at rest
Describe what happens to a stationary object on a floor when a pushing force acts on it, and the pushing force is more significant than maximum friction
- surface will still oppose motion at maximum friction
- resultant force=remaining pushing force to specific direction
- resultant force in specific direction causes object to accelerate in specific direction
pressure
force appplied perpendicular to surface of obj per unit area
pressure formula
force/contact area
p formula in symbols
p=F/A
where p = pressure in units of N/m^2
F=force in units of N
A is contact area in units of m^2
base SI unit for pressure
Pa (pascal) or N/m^2
what does pressure depend on
area of contact
force
area of contact (pressure)
pressure exerted on surface is greater when there is a smaller area of contact between object and surface for the same force
force (pressure)
with the same area of contact, pressure exerted is greater when force is greater
why does a body of liquid exert pressure
its weight
how does pressure in a liquid increase
with depth and density of liquid and with gravitational field strength
what is a turning effect of a force
when a force is applied on an object off centre, it can make the object to turn about a point called the pivot
can we gain or lose energy?
no. we can only change it from one form to another
does the total amount of energy before and after the energy transfer change?
no. this means the total amount of energy has been conserved. this is known as the principle of conservation of energy
what does the principle of conservation of energy state
energy cannot be created nor destroyed
energy can only be converted from one form to another
conservation of energy in an object in vertical motion (thrown) (negligible air resistance)
- KE (leaving hand)
- less KE, more GPE (GPE increasing) (in the air going upwards)
- only GPE (highest point)
- more KE, less GPE (GPE increasing) (in air going downwards)
- only KE (just before landing on hand)
TOTAL ENERGY = KE + GPE
total energy remains CONSTANT THROUGHOUT MOTION
conservation of energy in an object in vertical motion (thrown) (air resistance present)
- KE (leaving hand)
- less KE, more GPE and thermal energy (GPE increasing) (in the air going upwards)
- only GPE (highest point)
- more KE, less GPE (GPE increasing) (in air going downwards)
- only KE (just before landing on hand)
thermal energy is present throughout
TOTAL ENERGY = KE + GPE + THERMAL ENERGY
total energy remains CONSTANT THROUGHOUT MOTION
sum of KE and GPE decreases during motion.
compare and contrast the magnitude of KE of parachutist when air resistance is present vs when it is negligible
- KE inc from highest point to lowest point (compare)
- KE inc bc parachutist is moving with inc speed (explain)
- KE at each point is higher when air resistance is negligible (contrast)
- bc all GPE is converted to KE when air resistance is negligible (explain 1)
- bc all GPE is converted to KE and thermal energy when air resistance present. results in smaller magnitude of KE (explain 2)
does principle of conservation of energy aplly when there is air resistance
yes. GPE converted to KE and thermal energy. energy is not lost, rather converted
work definition
product of force and distance moved in direction of force
work formula
work = F x d
where work = word done by constant force in joules (J)
F = constant force in N
d = distance moved in m
when is there no work done
- obj does not move even with constant force applied
- obj moves at constant speed when there is no force acting on it
- obj moves perpendicular to force at a constant speed
does speed of doing work affect work done? why?
no. work = F x d and speed is not involved.. d is still the same. time taken does not affect work done
classify sources of energy
renewable
not renewable
renewable energy def
energy that is replenished/resupplied faster than it is being used up
non-renewable energy def
energy that is used up faster than it can be replenished or resupplied
non renewable sources of energy
fossil fuels
nuclear energy
renewable sources of energy
biofuels
wind
hydropower
geothermal power
solar power
unique pros and cons of nuclear energy
pros
do not emit greenhouse gases
do not emit gases that cause acid rain
1kg of nuclear fuelproduces millions of times more energy than 1kg coal
cons
limited supply
large amts of radioactive material will be released into environment if leak occurs
nuclear waste remains radioactive
removing nuclear plant is expensive
pros and cons of fossil fuels
pros
relatively cheap and easy to obtain
a lot of infrastructure is designed to work on fossil fuels
cons
limited supply
coal and oil release harmful gases when they burn which can cause breathing issues and acid rain
release greenhouse gases and increases rate of global warming
pros and cons of biofuels
pros
crops can be grown specifically for biofuels
cheap
readily available
plants they are made from absorb some co2 when grown
cons
decrease biodiversity
takes up land
remove nutrients from soil that can be used to grow food
pros and cons of wind
pros
no fuel costs
no harmful polluting gases produced
cons
noisy
may spoil view
amount of electricity gathered depends on wind strength
pros and cons of hydropower
pros
no fuel costs
no harmful polluting gases produced
tidal barrages and hydroelectric power stations are very reliable, easily switched on
cons
difficult to make wave machines big enough
tidal barrages derstroy natural habitats
dams flood farm land
pushes ppl from homes
rotting vegetation releases methane
pros and cons of geothermal power
pros
no fuel costs
no harmful gases produced
cons
most places are not suitable to exploit this power
pros and cons of solar power
pros
no fuel costs
no harmful gases produced
cons
may only produce very hot water when sunny
may need conventional heater in colder areas
although warm water can e produced on cloudy days, solar panels do not work at night.
