# Tag Info

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You blow away the flame from its fuel source. If you would blow less hard the flame might burn harder because more air is supplied to the flame (similar to a Bunsen burner). Because normally the flame of a candle gets its oxygen through a conventional airflow generated by the heat of the frame. The reason why the flame is blown away from the candle is ...

15

Combustion is a gas phase reaction. There are two requirements to generate a stable flame. Firstly the temperature must be high enough to vapourise the combustible material (wax in this case), and secondly the temperature must be high enough to generate the activation energy needed for the reaction. Heat is needed because gas phase molecules of wax and ...

5

If you look closely at the candle flame, you will notice that the flame hovers just over the wick, but does not touch it. This is because the flame is boiling the wax, which becomes a vapor, which then burns. All of these processes are driven by the heat from the flame. As you blow on the flame, you moving it away from the wax and disrupt this process. ...

3

This is quite humorous. In an 1883 offical US military publication, "Weather Proverbs" by 1st Lt. Dunwoody, at page 107 it is stated "When coffee bubbles collect in the centre of the cup expect fair weather. When they adhere to the cup, forming a ring, expect rain." This is the converse of the lifehack proverb! In 1997 Dave Thurlow, using a grant ...

2

There is no stupid question when it comes to genuinely trying to understand physics. Pressure is the result of molecules smashing against the walls of their enclosure. Except at zero Kelvin, there is always some kind of erratic movement which increases with temperature. For a given number of molecules in an enclosure, the smaller it gets and the more impacts ...

1

As fibonatic noted, you are blowing the flame activity away from the wick, but that's not the entire story: if the wick were still the same temperature it would immediately reignite. You are super-cooling the system by introducing a large mass which can't be heated enough to sustain the fire in time. This is, incidentally, one of the primary reasons why ...

1

Using Bernoulli you get: $$\frac{P_1}{\rho} + \frac{1}{2}v_1^2 = \frac{P_2}{\rho} + \frac{1}{2}v_2^2$$ Using your formula: $\displaystyle{c_s^2 + \frac{1}{2}v_1^2 = c_s^2 + \frac{1}{2}v_2^2}$ and this implies: $v_1 = v_2$ From mass continuity: $v_1 \times A_1 = v1 \times A_2$, so $A_1=A_2$, which is a false. There is clearly a misinterpretation. ...

1

In short if pipe A is much shorter than B, and both A and B have the same size and outlet pressure (aka back pressure), then pipe A and B will have identical pressure drop and pipe A will have a higher flow rate. Given a fixed inlet and outlet pressure, the pressure drop is also fixed ($\Delta P = P_{inlet} - P_{outlet}$) and therefore the flow in the two ...

1

Is it correct that the zero atmospheric pressure occurs at A? Yes, approximately. In a real system the pressure at A would equal the vapor pressure of the liquid. Your "other resources" are referring to the pressure of air in the atmosphere. In the problem, the diagram represents a situation like mercury in a barometer, where the weight of the mercury ...

1

Normally when compressing a gas the temperature increases. If you assume adiabatic compression, the law is $PV^\gamma=k$, where $\gamma=\frac {C_P}{C_V}$ is the ratio of specific heats and is usually about $1.4$ for air. Then, as shown here $\frac {T_2}{T_1}=\left(\frac {P_2}{P_1}\right)^{\gamma-\frac 1\gamma}$ This assumes you don't leak heat to the ...

1

A force is a vector. It represents a value and a direction. Pressure applied on a small surface results in a force applied in the direction perpendicular to the small surface and with value $F=P\, A$ where $P$ is pressure and $A$ is a small area. If you have an object, where low pressure is applied on a large area on one side, but high pressure is applied ...

1

In physics, pressure, $p$, is a Force, $F$, per unit Area, $A$. Where: $p=F/A$ We can see from the simple formula that to increase pressure we can increase the force or decrease the area. The example which you gave of a paper pin demonstrates mechanical pressure, by lowering the surface area of the end of a pin we can more easily penetrate the paper ...

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