chapter 15 forces and matter Flashcards
what is elastic distortion
an object has been elastically distorted if it can go back to its original shape and length after the force has been removed
what is inelastic distortion
an object has been in-elastically distorted if it doesn’t return t its original shape and length after the force has been removed
what is elastic limit
the point where an object stops distorting elastically and and begins to distort inelasticaly
what is the linear elastic distortion and spring constant equation
F = F * x
spring constant x extension
what is the equation for work done in stretching a spring
E= 0.5 x k * x2
describe the difference between linear and non-linear relationships between force and extension
linear- the extension of a spring is directly proportional to the force applied to it (straight line on graph)
non linear- there is a limit to the amount of force you can apply to an object for the extension to keep on increasing proportionally. Where the graph curves shows the maximum force and that the extension is no longer proportional to the force, the object stretches more for each unit increase in force. This point is known as the limit of proportionality.
what is hookes law
when an elastic object such as a spring is stretched, the increased length is called its extension. The extension of an elastic object is directly proportional to the force applied to it
explain why atmospheric pressure varies with height above the earths surface with reference to a simple model of the earths atmosphere
The atmosphere is thin compared to size of earth and becomes less dense as the altitude increases. Atmospheric pressure decreases as the height of a surface above ground level increases. This is because, as the altitude increases…
The number of air molecules decreases, the weight of the air decreases, there is less air above a surface.
why doe aircrafts that fly at high altitudes need to be pressurised
if the air pressure is too low, humans cannot take in Oxygen quickly enough to meet their bodies needs
what is the pressure of a fluid due to
the pressure in a fluid is caused by the particles that make up the fluid. These particles have a disordered motion so the presure acts equally in all directions. 3 factors affect the pressure in a fluid
1- the depth the pressure is measured at
2- the density of the fluid
3- the gravitational field stength
what does the pressure in a fluid cause
a force normal to any surface
explain how pressure is related to force and area
if the surface area is smaller the pressure will be greater for example- if i exert a force of 20 N on 10m2 = 2Pa but if the surface area was 5m2 instead the pressure would be 4Pa
what is the pressure equation
F
P= _
A
what is pressure measured in
Pa Pascal
what is area of surface measured in
meters squared
pressure in fluids =
increases with depth and density as there is an increase in fluid above. In a fluids with a greater density, the same volume of fluid above will have a greater weight, and so the pressure will be greater
what is a fluid
all gaseous materials and some liquid materials
what is upthrust equal to
the weight of fluid displaced
Explain why the pressure in liquids varies with density and depth
An increase in hydro-static pressure, the force per unit area exerted by a liquid on a n object. The deeper you go under the sea, the greater the pressure of the water pushing down on you. At high pressures density increases.
what is hydro-static pressure
the pressure that is exerted by a fluid at equilibrium at a given point within a fluids, due to the force of gravity. It increases in proportion to depth measured from the surface because of the increasing weight of the fluid exerting downward force from above
What is the equation used to calculate the magnitude of the pressure in liquids and calculate the differences in pressure at different depths in a liquid
P= h x d x g
Explain why an object in a fluids is subject to an upwards force (upthrust)
when an object is submerged in a fluid (partially or completely) the pressure of the fluid exerts a force on it from every direction. Pressure increases with depth, so the force exerted on the bottom of the object is larger than the force acting on the top of the object. This causes a resultant force upwards known as upthrust.
Explain how factors (upthrust, weight, density of fluid) influence whether an object will float or sink
in the upthrust of an object is equal to the objects weight, then the forces balance and the object floats.
If an objects weight is more than the upthrust, the object sinks. This means whether or not an object floats depends on its density.
An object that is less dense than the fluid it is placed in displaces a volume of fluid that is equal to its weight before it is completely submerged. The objects weight is equal to the upthrust so it floats.
An object that is denser than the fluid is is placed in is unable to displace enough fluid to equal its weight. This means that its weight is always larger than the upthrust so it sinks
what does buoyancy force mean
same as upthrust
how do submarines use upthrust
Submarines make use of upthrust. To sink, large tanks are filled with water to increase the weight of the submarine so that is is more than the upthrust. To rise to the surface, the tanks are filled with compressed air to reduce the weight so it is less than the upthrust.
what is upthrust
the upward force on the object provided by the liquid because the object has ‘displaced’ some of the fluid.
