Mass VS Weight

If we jump in a moving vehicle, will we land at the same spot?

Answer: Yes!

Thanks to RELATIVE MOTION, we will land at the same spot.

Motion is relative

All motion is relative to the observer or to some fixed object. When you see a car drive by, it is moving with respect to you. If you are in a car that is going at the same speed, the other car will not by moving with respect to you. But both cars are moving with respect to the ground.

Point of reference

In talking about motion, it is important to indicate your point of reference. In the case of moving automobiles, it is usually assumed the speed is with respect to the ground. But there are situations where the speed or velocity may be with respect to another object or an observer.

For example, suppose a car was traveling at 60 miles per hour (mph) and hit another car, but there was hardly a dent. The reason is that the second car was traveling in the same direction at 59 mph, so the car was going only 1 mph with respect to the second car when it hit it.

Sun looks like it is moving in the sky

Another example of relative motion is how the sun appears to move across the sky, when the earth is actually spinning and causing that apparent motion.

Usually, we consider motion with respect to the ground or the Earth. Within the Universe there is no real fixed point. The basis for Einstein's Theory of Relativityis that all motion is relative to what you define as a fixed point.

Reference:http://www.school-for-champions.com/science/motion.htm

Example:

You are in a train and you jump up. Where will you land?

You will land at the same spot because the train is moving in respect with the ground or train tracks but, the train is not moving in respect to you. See the part about Motion is relative.

Something interesting: Archimedes ancient death ray

The Archimedes Heat Ray – myth or reality?

Archimedes may have used mirrors acting collectively as a parabolic reflector to burn ships attacking Syracuse.

The 2nd century AD author Lucian wrote that during the Siege of Syracuse (c. 214–212 BC), Archimedes destroyed enemy ships with fire. Centuries later, Anthemius of Trallesmentions burning-glasses as Archimedes' weapon.^[25] The device, sometimes called the "Archimedes heat ray", was used to focus sunlight onto approaching ships, causing them to catch fire.

This purported weapon has been the subject of ongoing debate about its credibility since the Renaissance. René Descartes rejected it as false, while modern researchers have attempted to recreate the effect using only the means that would have been available to Archimedes.^[26] It has been suggested that a large array of highly polished bronze or coppershields acting as mirrors could have been employed to focus sunlight onto a ship. This would have used the principle of the parabolic reflector in a manner similar to a solar furnace.

A test of the Archimedes heat ray was carried out in 1973 by the Greek scientist Ioannis Sakkas. The experiment took place at the Skaramagas naval base outside Athens. On this occasion 70 mirrors were used, each with a copper coating and a size of around five by three feet (1.5 by 1 m). The mirrors were pointed at a plywood mock-up of a Roman warship at a distance of around 160 feet (50 m). When the mirrors were focused accurately, the ship burst into flames within a few seconds. The plywood ship had a coating of tar paint, which may have aided combustion.^[27]

In October 2005 a group of students from the Massachusetts Institute of Technology carried out an experiment with 127 one-foot (30 cm) square mirror tiles, focused on a mock-up wooden ship at a range of around 100 feet (30 m). Flames broke out on a patch of the ship, but only after the sky had been cloudless and the ship had remained stationary for around ten minutes. It was concluded that the device was a feasible weapon under these conditions. The MIT group repeated the experiment for the television showMythBusters, using a wooden fishing boat in San Francisco as the target. Again some charring occurred, along with a small amount of flame. In order to catch fire, wood needs to reach its flash point, which is around 300 degrees Celsius (570 °F).^[28]

When MythBusters broadcast the result of the San Francisco experiment in January 2006, the claim was placed in the category of "busted" (or failed) because of the length of time and the ideal weather conditions required for combustion to occur. It was also pointed out that since Syracuse faces the sea towards the east, the Roman fleet would have had to attack during the morning for optimal gathering of light by the mirrors. MythBusters also pointed out that conventional weaponry, such as flaming arrows or bolts from a catapult, would have been a far easier way of setting a ship on fire at short distances.^[1]

source: http://en.wikipedia.org/wiki/Archimedes

Rate

Rate is a ratio between two measurements, often with different units.. When we use the word rate, we usually mean how one quantity changes with time. The unit or quantity in respect of which something is changing is not specified, usually the rate is per unit time. However, a rate of change can be specified per unit time, or per unit of length or mass or another quantity. The most common type of rate is "per unit time", such as speed, heart rate and flux. Rates that have a non-time denominator include exchange rates, literacy rates and electric flux.

In describing the units of a rate, the word "per" is used to separate the units of the two measurements used to calculate the rate (for example a heart rate is expressed "beats per minute"). A rate defined using two numbers of the same units (such as tax rates) or counts (such as literacy rate) will result in a dimensionless quantity, which can be expressed as a percentage (for example, the globalliteracy rate in 1998 was 80%) or fraction or as a multiple.

Often "rate" is a synonym of rhythm or frequency, a count per second (i.e. Hertz) e.g. radio frequencies or heart rate or sample rate.

A rate of change can be formally defined in two ways:^[2]

where f(x) is the function with respect to x over the interval from a to a+h. An instantaneous rate of change is equivalent to aderivative.

An example to contrast the differences between the average and instantaneous definitions: the speed of a car can be calculated:

1. An average rate can be calculated using the total distance travelled between a and b, divided by the travel time
2. An instantaneous rate can be determined by viewing a speedometer

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Speed

Speed is a rate of progress. It is a measure of how fast or slow an object is moving. Because speed may vary over the duration of a journey, we use average speed to simplify calculations. Average speed is calculated by distance over time. The S.I. unit of length is metre (m) while the S.I. unit of time is seconds (s). Hence, the S.I. unit of speed is metre per second (m/s). Other common units are centimetre per scond (cm/s) and kilometres per hour (km/h).

Time

Time is the duration of an event. Before watches and clocks were invented, people had to depend on primitive methods of measuring time. For instance, knots were tied at regular spaces on a length of rope. The rope was set alight at one end. In this way, one could measure hoe long an event took by the number of knots burnt. Similarly, incense sticks were used in Chinese rituals sometimes.

However, such methods gave inaccurate measurements of time. Over the centuries, man has developed more accurate ways of measuring time.

Question : Why do we need a standard unit of time?

Answer: Humans experience time differently depending on their surroundings or emotions. For example, doing absolutely nothing (besides breathing) for one minute might seem a long time. However, playing a computer game for one hour seems like a short time, especially when we are so engrossed in it.

Units of time

The S.i. unit of time is seconds (s). There are other units of time such as minutes (min), hour (h) and millisecond (ms).

Question: How do we measure time accurately?

Answer: There are instruments to help us measure time. Watches and clocks are everyday instruments that we use to measure the time. However, these are not sufficiently accurate for scientific purposes as they measure time to the nearest second. for example, To measure how fast a gas is given off during a chemical reaction. Therefore we need to use a stopwatch.

Stopwatches

There are two types of stopwatches, the mechanical one and the electronic one.

Mechanical stopwatches

The mechanical stopwatch has a minute scale and a second scale. The smallest division on the mechanical stopwatch is 0.1 seconds. Hence, it is accurate to 0.1s.

Using the mechanical stopwatch:

Step 1: Press the operating button to start the stopwatch.

Step 2: Press the operating button again to stop the timing.

Step 3: Press the reset button to reset the stopwatch back to zero. It is ready to be used again.

Electronic stopwatches

The electronic stopwatch is more accurate than the mechanical stopwatch. It can measure time intervals accurate to 0.01s. Unlike the mechanical stopwatch, it can also record the time interval in hours.

Using the electronic stopwatch:

Step 1: Press the start/stop button to start the stopwatch.

Step 2: Press the start/stop button again to stop the timing

Step 3: Press the reset button to reset the stopwatch.

Hertbeat

By measuring our resting heart rate, we can monitor improvements to our health and fitness level. Many of us will enter into fitness and health routines that involve measuring our weight, body fat levels, and even our running times. And as we get fitter, one of the most important improvements can often go unmeasured: our heart rate.

Our heart beats all day long whether we’re moving, eating, sleeping, or standing still. And with each stroke, our heart pumps blood through our system carrying vital oxygen and fuel, and carrying out waste products. A heart that’s in good condition can do more with one beat than a heart that’s not as conditioned. This is why conditioned athletes have resting heart rates between 40 - 50 beats per minute which is well below the average of 70 bpm (males) and 75 bpm (females).

Most of us gauge our health and fitness by the bathroom scale. And while body weight is an important aspect to measure, there are many other improvements that can be measured too. Just as measuring body fat is a way to track our fitness improvement, measuring our resting heart rate is a way for us to see the strengthening of our heart muscle.

Many athletes use heart rate monitors to track their workout intensity. Using the formula of: Maximum Heart Rate (MHR) = 220 – age…athletes can calculate their intensity level by dividing their workout heart rate by their MHR. For example, a 35 year-old has a MHR of 185 bpm (220 – 35). If they’re working out at an average of 148 bpm, then their workout intensity is approximately 80% of our MHR (148/185 = 0.8 = 80%). As we train in the 55% - 85% of our MHR range, our heart and cardiovascular system gets stronger. And as our heart gets stronger, our heart rate while resting gets lower.

The best time to measure your resting heart rate is first thing in the morning…while still in bed. Take your forefinger and middle finger and place them on your wrist, neck or temple where your pulse can be felt the strongest. Looking at your wristwatch or a clock with a second hand, count the number of beats in a 15 or 30-second period. Multiply this number by 4 for 15 seconds or 2 for 30 seconds to get the number of beats per minute (bpm). This is your resting heart rate.

In recent years, there have been statistical links established between resting heart rate and longevity. There are even calculators out there that predict your life expectancy from your age and resting heart rate. It’s not a hard measurement to take and it’s a great feeling as you watch the number go down over time, knowing that your heart is getting stronger and healthier. So how do you reduce your resting heart rate? Exercise! Cardiovascular exercise raises your heart rate in that 55% - 85% range discussed above. You can do this by walking, running, swimming, hiking, or using cardio equipment at the gym. You can measure your pulse manually or buy a heart rate monitor to determine your workout intensity.

Source:http://www.the-fitness-motivator.com/resting-heart-rate.html