Forces (5) - Pt2 Flashcards
What’s the limit of proportionality?
The point on a extension-force graph, where the extension is no longer proportional to the force
What’s the formula to find elastic potential energy?
Elastic potential energy (J) = 1/2 x spring constant (N/m) x Extension (m)2
Ee = 1/2Ke2
In elastic deformation what’s the relationship between work done and elastic potential energy stored?
the work done on the spring and the elastic potential energy stored are equal.
What’s a moment?
A force or several forces which cause an object to rotate.
The turning effect of a force is called its moment
What formula gives you the size of the moment?
Moment of a force (Nm) = Force (N) x Distance (m)-the
Perpendicular distance from the pivot to the line of action of the force
M=Fd
Give an example of a moment? And how would you make the moment larger?
- The force on the spanner causes a moment on the nut (acting as a pivot)
- a larger force or a longer distance (spanner) would mean a larger moment
What would you do (that doesn’t affect the force or distance) to get the maximum moment?
Push at right angles (perpendicular) to the spanner
Pushing at another angle would mean a smaller distance and so a smaller moment.
If an object is balanced, the total clockwise moment about a pivot equals the ….
Anticlockwise moment
What are simple lever and a simple gear system used for?
to transmit the rotational effects of forces.
How do levers work?
- they increase the distance from the pivot at which the force is applied (M=Fd so less force for the same moment)
- levers make it easier to do work
Explain how gears transmit rotational effects
- the teeth of the gears interlock, causing each other to turn in opposite directions
- different sized gears can Change the moment of the force
- a force transmitted to a larger gear will cause a bigger moment as the distance to the pivot is greater
What fluids?
- substances that can flow (liquid/gas) because their particles move around
- these move around and collide with surfaces and other particles
- the particles have a mass and so exert a force when they collide, exerting pressure
What’s pressure?
Force per unit area
What’s the pressure of a fluid?
A force exerted at right angles (normal)to any surface in contact with the fluid
How can you calculate the pressure at the surface of a fluid?
Pressure (Pa) = Force normal to a surface (N)/ Area if that surface (m*2)
P= F/A
What’s density?
What’s the density of a liquid?
What’s the density of a gas?
- how close together the particles in a substance are
- in a liquid the density is uniform and doesn’t vary with shape or size
- the density of a gas can vary though
Explain what the pressure in a liquid depends on?
- the denser a liquid the more particles in a certain place so they collide more, so it increases the pressure
- increasing the depth of a liquid increases the number of particles above the liquid the weight of these parties add to the pressure
- so pressure in a liquid depends on depth and density
How do you find the pressure of a liquid?
Pressure (Pa) = height of the column of liquid (the depth)(m) x Density of the liquid (kg/m*3) x gravitational fried strength (N/kg)
P = h roh g
Define upthrust
- upthrust is equal to the weight of fluid that has been displaced by the object
- a submerged object experiences a greater pressure on the bottom surface than on the top surface. This creates a resultant force upwards. This force is called the upthrust.
What’s happening when an object floats?
The upthrust is equal to the objects weight
The forces are balanced so the object floats
What’s happening when an object sinks?
The objects weight is more than the upthrust so the object sinks
In terms of density explain how an object floats?
- An object less dense then the fluid it’s in weighs less than the equivalent volume of fluid
- this means it displaces a volume of a fluid that’s equal to its weight
- the objects weight is equal to the upthrust so it floats
Explain in terms of density why an object sinks?
- An object denser than the fluid it’s in is unable to displace enough fluid to equal its weight
- This means the weight is larger than the up thrust so it sinks
Explain how submarines use upthrust?
- to sink they fill large tanks with water to increase the weight of the submarine so it’s more than the upthrust
- to rise the tanks are filled with compressed air to reduce the weight so that it’s less than the upthrust
What’s the atmosphere?
A layer of air that surrounds Earth. It’s thin compared to the size of earth
What’s atmospheric pressure?
- created on a surface by air molecules colliding with the surface
- as the a,titube increases the atmospheric pressure decreases
- as the altitude increases, the atmosphere gets ,ses dense so there’s fewer air molecules that can collide with the surface
- there’s also fewer air molecules above the surface as the altitude increases this means the weight of air above it decreases with altitude
What’s the difference between displacement and distance?
Distance is a scalar it doesn’t involve direction. It’s how far an object moves.
Displacement is a vector it includes both the distance and the direction of that straight line.
What’s the difference between speed and velocity?
Speed is scalar
Velocity is a vector
What’s the formula the links speed, time and distance?
Distance (m) = speed (m/s) x time (s)
S=vt
What’s the speed of a person:
- walking
- running
- cycling
- walking: 1.5 m/s
- running: 3m/s
- cycling: 6m/s
