chapter 15 forces and matter

Question 1

what is elastic distortion

Answer 1

an object has been elastically distorted if it can go back to its original shape and length after the force has been removed

Question 2

what is inelastic distortion

Answer 2

an object has been in-elastically distorted if it doesn’t return t its original shape and length after the force has been removed

Question 3

what is elastic limit

Answer 3

the point where an object stops distorting elastically and and begins to distort inelasticaly

Question 4

what is the linear elastic distortion and spring constant equation

Answer 4

F = F * x

spring constant x extension

Question 5

what is the equation for work done in stretching a spring

Answer 5

E= 0.5 x k * x2

Question 6

describe the difference between linear and non-linear relationships between force and extension

Answer 6

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.

Question 7

what is hookes law

Answer 7

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

Question 8

explain why atmospheric pressure varies with height above the earths surface with reference to a simple model of the earths atmosphere

Answer 8

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.

Question 9

why doe aircrafts that fly at high altitudes need to be pressurised

Answer 9

if the air pressure is too low, humans cannot take in Oxygen quickly enough to meet their bodies needs

Question 10

what is the pressure of a fluid due to

Answer 10

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

Question 11

what does the pressure in a fluid cause

Answer 11

a force normal to any surface

Question 12

explain how pressure is related to force and area

Answer 12

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

Question 13

what is the pressure equation

Answer 13

F
P= _
A

Question 14

what is pressure measured in

Answer 14

Pa Pascal

Question 15

what is area of surface measured in

Answer 15

meters squared

Question 16

pressure in fluids =

Answer 16

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

Question 17

what is a fluid

Answer 17

all gaseous materials and some liquid materials

Question 18

what is upthrust equal to

Answer 18

the weight of fluid displaced

Question 19

Explain why the pressure in liquids varies with density and depth

Answer 19

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.

Question 20

what is hydro-static pressure

Answer 20

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

Question 21

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

Answer 21

P= h x d x g

Question 22

Explain why an object in a fluids is subject to an upwards force (upthrust)

Answer 22

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.

Question 23

Explain how factors (upthrust, weight, density of fluid) influence whether an object will float or sink

Answer 23

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

Question 24

what does buoyancy force mean

Answer 24

same as upthrust

Question 25

how do submarines use upthrust

Answer 25

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.

Question 26

what is upthrust

Answer 26

the upward force on the object provided by the liquid because the object has ‘displaced’ some of the fluid.