All categories

1 year ago

3. If nothing can ever be at absolute zero, why does the concept exist?

1 answer:

6 0

The reason has to do with the amount of work necessary to remove heat from a substance, which increases substantially the colder you try to go. To reach zero kelvins, you would require an infinite amount of work.

You might be interested in

Indicate on a tensile curve such quantities as yield stress, Young's modulus, UTS, toughness, point of necking, point of fractur

Illusion [34]

Explanation:

Step1

In the stress-strain curve of any material, the yield stress is the maximum stress at which material starts yielding.

Step2

Young’s modulus is the constant of proportionality of stress and strain according to hooks law. It is the slope of the slope of the stress-strain curve of the any material under proportional limit.

Step3

Ultimate tensile stress is the maximum stress that induced in the material under application of load.

Step4

Toughness is the strain energy per unit volume up to the fracture point of the stress-strain diagram of any material. This is the area under the curve of stress-strain.

Step5

Point of necking is the point where any material starts necking under application of load in necking region of the stress-strain curve.

Step6

Fracture point is the last point of the stress-strain curve where component fractures under application of load.

All the parameters are shown in below stress-strain curve:

8 0

3 years ago

Define the terms (a) thermal conductivity, (b) heat capacity and (c) thermal diffusivity

IceJOKER [234]

Explanation:

(a)

The measure of material's ability to conduct thermal energy (heat) is known as thermal conductivity. For examples, metals have high thermal conductivity, it means that they are very efficient at conducting heat. The SI unit of heat capacity is W/m.K.

The expression for thermal conductivity is:

$q=-\kappa \bigtriangledown T$

Where,

q is the heat flux

$\kappa$ is the thermal conductivity

$\bigtriangledown T$ is the temperature gradient.

(b)

Heat capacity for a substance is defined as the ratio of the amount of energy required to change the temperature of the substance and the magnitude of temperature change. The SI unit of heat capacity is J/K.

The expression for Heat capacity is:

$C=\frac{E}{\Delta T}$

Where,

C is the Heat capacity

E is the energy absorbed/released

$\Delta T$ is the change in temperature

(c)

Thermal diffusivity is defined as the thermal conductivity divided by specific heat capacity at constant pressure and its density. The Si unit of thermal diffusivity is m²/s.

The expression for thermal diffusivity is:

$\alpha=\frac{\kappa}{C_p \times \rho}$

Where,

$\alpha$ is thermal diffusivity

$\kappa$ is the thermal conductivity

$C_p$ is specific heat capacity at constant pressure

$\rho$ is density

6 0

2 years ago

The tropics receive more heat from the sun than is radiated away from the tropics, and polar regions radiate more than they rece

IRINA_888 [86]

Answer:

It is a well known fact that the earth rotates around the sun in an inclined axis which is approximately 23 degree. The inclined nature of earth axis causes variation in the solar heat received at any place on the earth surface. The hemisphere facing the sun due to this axial tilt, gets higher sun energy as compared to the opposite side. The hemisphere which faces the sun will experience summer whereas the hemisphere away from sun will experience winter.

In each of the hemisphere the polar areas will receive higher radiation and longer daytime during the summer season. However it has been observed that there is difference in radiation received at different areas of earth surface and radiated. The tropical areas have lower reflectance and thus a large part of incoming solar radiation have been absorbed along the tropics. The poles though have longer daytime during summer and hence greater solar radiation but due to high reflectance radiate more energy. Thus the tropical areas have surplus energy as compared to deficit energy areas of poles. This difference in energy creates a heat imbalance.

This net heat difference between poles and equator gives rise to a global circulation system leading to flow of heat from the net energy excess areas to deficit areas. This circulation takes place through atmosphere as well as oceans and different process of climate viz. evaporation, transpiration, rainfall, wind, convection, oceanic circulations etc work as tools of this system

4 0

2 years ago

Give two causes that can result in surface cracking on extruded products.

Andreas93 [3]

Answer:

1. High friction

2. High extrusion temperature

Explanation:

Surface cracking on extruded products are defects or breakage on the surface of the extruded parts. Such cracks are inter granular.

Surface cracking defects arises from very high work piece temperature that develops cracks on the surface of the work piece. Surface cracking appears when the extrusion speed is very high, that results in high strain rates and generates heat.

Other factors include very high friction that contributes to surface cracking an d chilling of the surface of high temperature billets.

6 0

2 years ago

When an object is moving, we use the following coefficient for friction calculations a)-μk b)-μs c)-γk d)- γs

Reika [66]

Answer: $\mu_{k}$

Explanation:

We use kinetic friction when a body is moving i.e. $\mu_{k}$ for calculations.

Static friction is used when a body is in rest while kinetic friction is used when a body is moving and its value is quite low as compared to static friction .

Static friction value increases as we apply more force while kinetic friction occurs when there is relative motion between bodies.

3 0

3 years ago