Momentum, Work and Energy
Momentum is a measurement of mass in motion: how much mass is in how much motion. The useful thing about momentum is its relationship to force. . space station and an astronaut needs to manually move a free-floating 4, kg space. First, it is technically a vector equation because the momentum of an object .. With the same force, this would be the same stopping distance. The car has a lower mass, so it must have a higher velocity in order to have the. rate of change of momentum = mass x rate of change of velocity. from falling to the floor, you do not move the box in the direction of that force, that is, upwards.
What are momentum and impulse?
It is only the overall net impulse that matters for understanding the motion of an object following an impulse. Watch this video on area under rate function to learn more about how to use the area under a curve to evaluate the product of the quantities on the axes.
The concept of impulse that is both external and internal to a system is also fundamental to understanding conservation of momentum. Momentum in space Most people are familiar with seeing astronauts working in orbit.
They appear to effortlessly push around freely floating objects. Because astronauts and the objects they are working with are both in free-fallthey do not have to contend with the force of gravity.
How is force related to the transfer of momentum? | How Things Fly
However, heavy moving objects still possess the same momentum that they do on earth, and it can be just as difficult to change this momentum. Suppose that an emergency occurs on a space station and an astronaut needs to manually move a free-floating 4, kg space capsule away from a docking area.
On earth, the astronaut knows she can hold a 50 kg weight above herself for 3 seconds. How quickly could she get the capsule moving? In other words, since these are vectors, they are of equal length but pointing in opposite directions. This means that for every bit of momentum A gains, B gains the negative of that.
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In other words, B loses momentum at exactly the rate A gains momentum so their total momentum remains the same. But this is true throughout the interaction process, from beginning to end. Therefore, the total momentum at the end must be what it was at the beginning.
You may be thinking at this point: Nevertheless, we do know that momentum will be conserved anyway, so if, for example, the two objects stick together, and no bits fly off, we can find their final velocity just from momentum conservation, without knowing any details of the collision. First, it only refers to physical work, of course, and second, something has to be accomplished.
Consider lifting the box of books to a high shelf. If you lift the box at a steady speed, the force you are exerting is just balancing off gravity, the weight of the box, otherwise the box would be accelerating. Putting these together, the definition of work is: To get a more quantitative idea of how much work is being done, we need to have some units to measure work. This unit of force is called one newton as we discussed in an earlier lecture.
Note that a one kilogram mass, when dropped, accelerates downwards at ten meters per second per second.
How is force related to momentum?
This means that its weight, its gravitational attraction towards the earth, must be equal to ten newtons. From this we can figure out that a one newton force equals the weight of grams, just less than a quarter of a pound, a stick of butter. The downward acceleration of a freely falling object, ten meters per second per second, is often written g for short.
Now back to work. In other words approximately lifting a stick of butter three feet. This unit of work is called one joule, in honor of an English brewer. To get some feeling for rate of work, consider walking upstairs. A typical step is eight inches, or one-fifth of a meter, so you will gain altitude at, say, two-fifths of a meter per second.Collisions: Crash Course Physics #10
Your weight is, say put in your own weight here! A common English unit of power is the horsepower, which is watts. Energy Energy is the ability to do work. For example, it takes work to drive a nail into a piece of wood—a force has to push the nail a certain distance, against the resistance of the wood.
A moving hammer, hitting the nail, can drive it in. A stationary hammer placed on the nail does nothing. Another way to drive the nail in, if you have a good aim, might be to simply drop the hammer onto the nail from some suitable height. By the time the hammer reaches the nail, it will have kinetic energy. It has this energy, of course, because the force of gravity its weight accelerated it as it came down.
Work had to be done in the first place to lift the hammer to the height from which it was dropped onto the nail. In fact, the work done in the initial lifting, force x distance, is just the weight of the hammer multiplied by the distance it is raised, in joules. But this is exactly the same amount of work as gravity does on the hammer in speeding it up during its fall onto the nail. Therefore, while the hammer is at the top, waiting to be dropped, it can be thought of as storing the work that was done in lifting it, which is ready to be released at any time.
To give an example, suppose we have a hammer of mass 2 kg, and we lift it up through 5 meters. This joules is now stored ready for use, that is, it is potential energy.
We say that the potential energy is transformed into kinetic energy, which is then spent driving in the nail. We should emphasize that both energy and work are measured in the same units, joules.
In the example above, doing work by lifting just adds energy to a body, so-called potential energy, equal to the amount of work done. From the above discussion, a mass of m kilograms has a weight of mg newtons. It follows that the work needed to raise it through a height h meters is force x distance, that is, weight x height, or mgh joules.