Forces and matter Flashcards
Stretching, bending, and compressing
More than one force has to be applied
If a single force is applied, the object will just move in the force’s direction. If forced inwards from opposite sides, the object (e.g. a spring) will compress
* If fixed at one end of the spring and a force is applied at the other, more than one force is still being applied to the spring (a reaction force from the fixed point)
Deformation
This means changing shape
Elastic Deformation
* The object returns to its original shape when the load has been removed
Eg. An elastic band
Plastic Deformation (distortions)
The object does not return to its original shape when the load has been removed
Eg. A spring when pulled too far
Hooke’s Law: The extension of a spring is directly proportional to the force applied.
Linear line section on a Force/Extension Graph
This is elastic
Following Hooke’s Law
Gradient is K (refer to equation above).
Elastic deformation
The point it stops being linear is the elastic limit
From then on. it does not obey Hooke’s Law
Non-Linear line section
Not elastic
Does not follow Hooke’s Law
Plastic Deformation
if shallow: lots of extension for not a lot of force, easy to stretch
If graph is just linear, with no “non-linear end section”
The material is “brittle, so snaps instead of stretches after the elastic limit
Atmospheric Pressure is the total weight of the air above a unit area at a certain altitude.
Therefore, atmospheric pressure decreases with increasing height above the Earth’s surface o The weight of the air is the force which causes the pressure
So with higher elevation, there are fewer air molecules above the unit area than the same area at lower heights, so there is less weight, so less pressure
Pressure in a fluid (Physics Only)
A fluid Is a liquid or a gas
Pressure of a gas (for example held in a balloon) depends on atmospheric pressure
The air exerts an inward force on the outer surface of the balloon, and if this force is greater than the outward force exerted by the gas particles inside, the balloon will
collapse.
In space there is a lower atmospheric pressure, so the gas inside exerts a greater force outward force on the balloon surface compared to the thinner air from the
outside. so the balloon can expand.
Increasing the amount of particles in the balloon (blowing into it) increases the amount of collisions the balloon surface experiences per second, so there is a greater pressure on the inside and the balloon will expand
Pressure in a fluid causes a force perpendicular to any surface
Pressure in Liquids Vary (Physics Only)
In fluids:
Deeper in a fluid you are, the greater the pressure.
Greater the amount of fluid above the object, so greater weight, so greater force felt, so greater pressure
Denser the fluid is, the greater the pressure
* mass = density × volume so greater density means greater weight of fluid on the object, so greater force and pressure
Factors that influence floating and sinking (Physics only)
An object floats, if its weight is less than the weight of the water it displaces
So a 1000kg boat will sink into the water until it has displaced 1000kg of water
* Providing the boat doesn’t completely submerge before it displaces this amount,
then it will float.
Pressure in a liquid varies with depth and density, and this leads to an upwards force on a partially submerged object.
The buoyancy force is the upwards force that counteracts the weight of the floating object
This force is equal to the weight of the fluid displaced by the object
A ping pong ball floats on water as its density is less than the density of the water, so for
rha
volume displaced, the weight of the equivalent amount of water is greater than the weight of the ping pong ball, so the resultant force is buoyancy, so it floats
Increasing the depth, the greater the weight of the water above you, so greater force felt, so greater pressure.
pressure due to a column of liquid = height of column × density of liquid × g
