Because one pole of the Earth's axis of rotation (the North one) points
almost exactly toward Polaris.
If Polaris had a pimple or a bump somewhere on its edge, you'd see
the bump rotate around the whole edge, like a clock, once a day. But
the whole star appears to stay in one place, because our axis points to it.
When air is blown across the top of an open <span>water bottle, air molecules in the bottle vibrate at a particular frequency and sound is produced in a process called "refraction".
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Answer:
refracción
Explanation:
I don't speak spanish but that's the answer
Answer:
The gravitational potential energy between two particles, if the distance between them is halved, is multiplied by 4 (option c).
Explanation:
The gravitational force is the force of mutual attraction that two objects with mass experience.
The Law of Universal Gravitation enunciated by Newton says that every material particle attracts any other material particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance that separates them. Mathematically this is expressed as:

where m1 and m2 are the masses of the objects, r the distance between them and G a universal constant that receives the name of constant of gravitation.
If the distance between two particles is reduced by half, then, where F' is the new value of the gravitational force:




F'=4*F
<u><em>
The gravitational potential energy between two particles, if the distance between them is halved, is multiplied by 4 (option c).</em></u>
Explanation:
Echoes occur due to the reflection of sound from any obstacle, but not all the reflected sound waves lead to the phenomenon of echo. For the echo to be heard it actually depends upon the human perception as well, human ears can encounter the difference between the sound wave directly form the source and the reflected sound waves only if there is a minimum time gap of one-tenth of a second. For this time gap in the atmosphere at normal temperature and pressure the obstacle must be at least 7 meters away from the sound source.