from the show Why do Men's Bits Shrink in the Cold? One thing I have wondered is how much does earth weigh? How many pounds does earth way, and if we don't yet know, do you think it would ever be possible to guess accurately? KEEP UP THE GREAT WORK!!! BenAnswer Chris -   The stated weight � mass, we should more accurately, of the Earth is about 6 x 1024 kilograms.  In other words, if you turn that into tons, it�s 6 with 21 zeros after it, tons.  So pretty heavy, but the big question is and this is where Dave can help me out, how do we actually know that something on the scale of the Earth that we can't physically put on a pair of scales, how do we know how much that weighs because Archimedes famously said, �If you give me a lever long enough and somewhere far enough away to stand, I could lift up the Earth� but how would we have calculated how much the earth actually weighs, Dave? Dave -   Well, the simple way of doing this is because anything with a mass affects everything around it due to gravity. 

If it�s something roughly spherically symmetrical, you can assume that all the mass is in the centre of the planet and it behaves as if it was all the mass is right in the centre, due to some neat bits of maths.  Basically, what you have to do is - if you know how much gravitational force a kilogram of anything will apply to another kilogram of anything, and you know how much force a kilogram of substance is being attracted to the Earth and you know how big the Earth is, you can work out how much mass must be in the Earth.  How To Clean Latex Paint From BathtubThe second part of that is really easy.  Laser Light Show For BedroomWorking out how much force a kilogram produces is really difficult because it�s about 10-11 Newtons at a metre between 2 kilograms.  Pallet Furniture Outdoor Sofa

It�s an incredibly tiny force and it wasn�t done until near the end of 19th century. Chris -   Henry Cavendish, wasn�t it?Indeed and you can work it out, and then from that, you can work out how heavy the Earth is, and from that, how heavy everything else is in the universe really. So, my company works with electric motors, and my boss wanted me to calculate how much weight could be lifted by a motor rated at 750W. I know that I can't just calculate the work done by it without any further specification of characteristics, but what I what to know is a couple of formulas that could get me there using measurable values, for example, i can measure current consumed when lifting a 10kg weight. Also, I'm open to suggestions, if you think there is an easier way to get where I want to, I am open to new ideas. homework-and-exercises newtonian-mechanics forces electricity weight There are two separate issues here. The maximum weight your motor will be able to lift depends on its torque.

The rate at which your motor can lift the weight depends on its power. The torque of the motor can be increased or decreased by running it through a gearbox, so in principle you could lift as big a weight as you want as long as you use a very low gear (and therefore lift the weight slowly). The rate of lifting is easier to be precise about. If you lift a mass $m$ through a height $h$ in a time $t$ the power required is: $$ W = \frac{mgh}{t} \tag{1} $$ or putting it another way, if you lift the mass at a velocity $v$ the power is: $$ W = mgv \tag{2} $$ (because v = h/t). So to take your example of a 10kg weight, to lift this at a speed of 1 m/s would require a power: $$ W = 10 \times 9.81 \times 1 = 98.1W $$ which is well within the power of your 750W motor. Alternatively you could flip this around and ask how fast you could lift the 10kg weight if you ran the motor at full power. Rearranging equation (2) gives: $$ v = \frac{W}{mg} = \frac{750}{10 \times 9.81} \approx 7.6 \text{m/s} $$

Browse other questions tagged homework-and-exercises newtonian-mechanics forces electricity weight or ask your own question.For many years residential air conditioners used pistons as metering devices, and you will still commonly encounter these systems. The piston looks like a small brass or bronze “bullet,” with a calibrated hole drilled through the center. The size of the hole, along with the pressure drop across the hole, determines how much refrigerant flows through the system. Most of the systems with piston metering devices are charged by the suction superheat method. Manufacturers of these systems typically provide a charging chart or slide rule to properly charge their systems. Sometimes these charts are available from your wholesaler. If you’re fortunate, they may be included inside the service panel of the unit that you’re servicing. Normally the charts will require an indoor wet bulb temperature reading as well as an outdoor dry bulb temperature reading. The indoor wet bulb reading reflects the total heat of the air and, therefore, the total loading on the indoor coil, both sensible and latent.

The outdoor dry bulb temperature will affect how well the system can reject heat to the outdoor air. In the case of the outdoor air there’s no latent heat involved. Once you determine the indoor wet bulb and outdoor dry bulb temperatures, check the manufacturer’s charging chart to determine the proper suction superheat. To measure suction superheat, attach your gauge manifold to the suction service port on the outdoor unit. Do not use the common suction pressure port on a heat pump because the pressure drop through the reversing valve will affect the pressure reading. Take the pressure reading and use a temperature-pressure chart to convert that reading to the saturated temperature of the refrigerant that the system uses. Note that most gauges have the commonly used refrigerants shown on the gauges. This is especially true of the newer digital gauges. Next, attach an accurate digital thermometer to the suction line near the suction gauge port. It’s usually best to insulate the thermometer probe so that it’s not affected by the ambient air.

The temperature that you measure should be warmer than the saturated refrigerant temperature. The difference between the saturated suction temperature and the measured suction line temperature is the suction superheat. Add refrigerant to lower the suction superheat. Recover refrigerant to increase the suction superheat. Note that you should never add refrigerant if the superheat is already 5F or less, even if the charging chart shows 0F. You don’t want to overcharge the system if your thermometer or gages are not perfectly accurate. Overcharging can damage the compressor and will also reduce both the capacity and efficiency of the system. Note that if the suction superheat is correct and the suction pressure is low, the system probably has low airflow. Correct the airflow problem and check the charge again. On many newer systems, especially high efficiency systems, thermostatic expansion valves (TXVs) are used. Expansion valve systems are normally charged by using the subcooling method.

Liquid sub-cooling is required so that you have only liquid entering the expansion valve with no bubbles present. Vapor bubbles present in the refrigerant will cause low refrigerant flow. Low refrigerant flow will cause a loss of capacity and efficiency in a cooling system. Liquid sub-cooling is normally measured at the liquid line service valve. The manufacturer will usually specify the required sub-cooling on the outdoor unit service panel. It’s usually between 5F and 15F, but always go by the manufacturer’s requirements. To measure liquid subcooling, attach your gauge manifold to the liquid line service port. If you use a quick-connect fitting on the end of your hose, make sure it’s a low-loss fitting. I’ve seen some quick-connect fittings that allow pressure loss, which can cause inaccuracies in the charging procedure. Take a pressure reading. Use a temperature-pressure chart to convert the pressure to the saturated condensing temperature of the refrigerant. Next, attach an accurate digital thermometer to the liquid line.

The temperature that you read with the thermometer should be lower than the saturated condensing temperature. The difference between the measured liquid line temperature and the saturated condensing temperature is the liquid subcooling. Add refrigerant to increase subcooling. Recover refrigerant to reduce subcooling. Note that if the subcooling and superheat are correct, and the suction pressure is low, the system probably has low air flow. When charging by the subcooling method, you should be sure to check the suction superheat as well. If the expansion valve goes bad, you can have a very low suction superheat when you have the proper subcooling. In some cases it’s not possible to achieve the required subcooling without having a superheat of zero degrees. If you get zero degrees superheat with a TXV, then the TXV is defective and will need to be replaced. One other method of charging is the weigh-in method. The weigh-in method can be very accurate if you know the exact length of the refrigerant lines.