P1D- Forces, energy, work, power and pressure Flashcards
What is a force
A force is a push or pull.
What are forces measured in
Newtons (N)
What effects can forces have
pushing, pulling, bending, stretching, squeezing tearing
What can forces do
change the size of an object
change the motion of an object
change the shape of an object
what are some examples of Non contact forces
Gravity
Magnetism
Electrostatic
What are some examples of Contact forces
friction
drag (air resistance)
upthrust
tension
What makes a force balanced?
Forces are balanced when they are equal in size and opposite in direction, causing no change in motion.
What are electrostatic forces
those between charges such as electrons. Like charges repel and unlike charges attract
What two factors determines whether a force will cause the object will move and the direction it does so?
The size and directions of forces
whats the force that causes all the objects in the universe to attract
gravity
what is the resultant force
the added up force that represents the combined effect of all forces acting on an object.
e.g Twelve husky dogs are pulling a sledge. The sledge is travelling to the right and each dog is pulling with a force of 50N. There is friction with the force of 250N that is trying to slow the sledge, and there fore must be pointing to the left.
The total force to the right (12x50)= 600N
The total force to the left is 250N
The resultant force = 600-250=350 to the right. (direction needed)
what does zero resultant force mean
object is at equilibrium
no acceleration- constant speed/stationary
the ________ varies with the load attached to it (______)
extension, force
What is the limit of proportionality
the point at which the extension is no longer proportional to the load- material starts behaving unpredictably.
When forces are balanced they are in _________
when forces are unbalanced they are in __________
equilibrium
disequilibrium
Whats an experiment to show hooke’s law?
- assemble the apparatus: ruler, spring, stand, clamp, masses
- take the first mass which consists of the hook and the base blate (100g) and measure the new position of the bottom end of the spring of the ruler. The difference in the reasings is the extension of the spring
- add masses one by one to the first one.
- Calculate the extension and plot a graph of extension
how is the graph drawn for hooke’s law
force (massxgravity)- on the y axis
extension- on the x axis
what is a spring that obeys hookes law known to perform
proportional behaviour
equation for hooke’s law
force (F)= spring constant (k) x extension of spring (x)
what is friction
a force that opposes motion
e.g air resistance
where can friction be useful
bicycle wheels and bicycle brake pads
what do forces have to be for an objects speed or direction of movement to change
unbalanced
Newtons second law equation
F=ma
Newton’s first law
Objects will remain at rest or move with a constant velocity unless acted on by resultant forces
Newton’s second law
The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the objects mass (F=ma)
for the equation to apply what conditions must ‘force’ and ‘mass’ meet?
mass is constant
force is constant
mass should always be in ______
kgs/g
whats newtons third law
for every action (force) in nature there is an equal and opposite reaction.
what is a moment
the turning effect produced when a force is exerted on an object
Examples of moments
door and door hinge
see saws
formula for moment of a force
size of moment (Nm): force (N) x perpendicular distance from pivot moment (m)
Fd
what does it mean if an object is not turning
the sum of clockwise moments about any pivot equals the sum of the anticlockwise moments about the same pivot
what is equilibrium
a state of balance or stability: no resultant force no resultant moment
what should you always include after writing the size of moment
clockwise/anticlockwise
what is the centre of mass
the point through which the weight of an object acts
How do you find the centre of mass of simple objects such as a piece of card
- hang up the object
- suspend a mass from the same place
- mark the position of the thread
- the centre of mass is somewhere along the line of the threat
- repear steps 1-3 with the object suspended from a different place
- the centre of mass is where the two lines meet
when is an object stable
when its centre of gravity lies above its base
where is the centre of gravity of a symmetrical object
at the point of symmetry
when is an object considered in stable equilibrium
when its difficult to topple
what is pressure
the ratio of force to area.
the equation for pressure
p=F/A
pressure measure in pascals
force: newtons
area: m^2
when is work done
when the application of a force results in movement
what does the amount of work done depend on
the magnitude of the force and the distance moved in the direction of the force
What is the equation for work done
Work (joules/ Nm)= Force (N) x distance moved in the direction of force (m)
how can work done be calculated when object is lifted vertically
the force moved is the weight of object
distance is the height (vertical distance)
When is more work done
when the mass is bigger or the object is raised further
what is potential energy
stored or hidden energy
when does a spring have elastic potential energy
when a spring is compressed or stretched
what can potential energy be transferred to
an object and make it move so give it kinetic energy
where can kinetic and potential energy be seen
energy transfers during the swing of a pendulum
at each end of its swing the pendulum has a maximum amount of gravitational potential energy and at the middle the potential energy has been transferred to kinetic.
an object gains ___________ potential energy as it gains __________. _________ has to be done to increase the height of the object above the ground. Therefore ________ in gravitational _________ energy = _____ ______ on that object against gravity.
gravitational
height
work
gain
potential
work done
formula for gravitational potential energy
potential energy (J) mgh -
m=mass (kg/g)
g= acceleration due to gravity
h=height (m)
formula for kinetic energy
k.e (j) = 1/2mv^2
m= mass (kg/g)
v= velocity (m/s)
what does the principle of conservation of energy state
energy can not be created or destroyed, it can only be transferred from one store to the other
energy can be _________ (spread out) to the _________ by heating and ___________
dissipated
surroundings
radiation
total mechanical energy formula
kinetic energy+ potential+ elastic
what is power
work done per unit time (energy transferred per unit time)
power formula
change in energy/time or work done/ time
what is power measured in
watts
what is energy efficiency
the ratio of the useful power or energy output from a system to its total power or energy input.
formula for energy efficiency
useful energy/total energy x 100
what should the total amount of energy transferred into the system equal to
the total amount of energy transferred away from the system
What is chemical potential energy?
It is energy stored in chemical bonds, such as in fossil fuels like coal, oil, and natural gas.
How is energy released from fuels?
Through combustion, where chemical bonds are broken, releasing heat energy.
How do waves generate energy?
The movement of waves drives turbines, which convert kinetic energy into electrical energy.
What is tidal energy?
Energy generated from the movement of water caused by tides, often using tidal barrages or underwater turbines.
Name one advantage of tidal energy.
It is renewable and predictable.
Name one disadvantage of wave energy
It can disrupt marine ecosystems and is location-dependent.
What is geothermal energy?
Energy from the heat stored in the Earth’s crust.
How is geothermal energy harnessed?
By using steam or hot water from underground to turn turbines and generate electricity.
Name one advantage of geothermal energy.
It is renewable and produces low emissions.
Name one disadvantage of geothermal energy.
It is limited to regions with geothermal activity.
How is nuclear energy generated?
By splitting atoms (nuclear fission) in a reactor to release heat, which produces steam to drive turbines.
What is one advantage of nuclear energy?
It produces large amounts of energy with no greenhouse gas emissions during operation.
What is one disadvantage of nuclear energy?
It generates radioactive waste that needs to be safely stored.
How is solar energy harnessed?
Using solar panels (photovoltaic cells) to convert sunlight into electricity or solar heaters for heat.
Name one advantage of solar energy.
It is renewable and abundant in sunny areas.
Name one disadvantage of solar energy.
It is weather-dependent and requires large areas for panels.
How is wind energy generated?
By using wind turbines that convert the kinetic energy of moving air into electrical energy.
What is one advantage of wind energy?
It is renewable and produces no greenhouse gas emissions.
What is one disadvantage of wind energy?
It is intermittent and depends on wind availability.
_________ energy -> ___________ energy
-> __________ energy
potential
kinetic
electrical/elastic
