Classical mechanics, physics and the theory of relativity use different concepts of time. The concept characterizes the sequence of events in space.
Speed, time and distance are physical quantities, interconnected by the process of movement. Distinguish between uniform and uniformly accelerated of the body. With uniform movement, the speed of the body is constant and does not change over time. With uniformly accelerated motion, the speed of the body changes with time. Let’s figure out how to find the time, knowing the magnitude of speed and distance.
General characteristics of time in physics
Speed, time and distance are physical indicators that are interconnected by the process of movement. In practice and theory, the uniform and uniformly accelerated motion of bodies is known. The first case describes the constancy of time, and the second – its change.
Basic concepts of time in physics
To measure time, you need to know common recurring events with the same period. It can be a change of day, night or season. To determine the unit of measurement of time (meter, hour, second), scientists turned to the most ancient sources of knowledge.
A year consists of twelve months or four seasons. This number of times in the spring, summer, winter and autumn periods, the main satellite of the Earth changes its phases.
Einstein’s theory of relativity changes the understanding of time, arguing that its progress is not universal and depends on who changes it. In such a picture of reality, the clock ticks at different speeds depending on who is wearing it.
Ancient system of calculus
Before the existence of our era, people tied the countdown to the movement of celestial bodies or events associated with them. The ancient peoples were looking for a basis for building their own numbering system. In Babylon, it was the number 60, thanks to which the circle contains 360 °, the degree is 60 minutes, and each of them consists of 60 seconds.
The first antique clocks are the solar yardsticks. Their action is based on the change in the length of the shadows of objects as the sun moves across the sky. Such a watch outwardly was a long pole stuck into the ground. The work of such mechanisms was not tied to the movement of the Sun, Moon or stars.
Physics indicators
There is no definite concept or class of time. The process continuity indicator can be calculated using a formula, analyzed on a graph or diagram.
Calculation definitions and concepts
Thermodynamics says that time cannot be returned. Its course depends on the movement of the frame of reference and can be instantaneous.
The periodic chain of events is calculated differently depending on the indicators. Dependent quantities:
- time;
- speed;
- distance.
The second is the standard unit of time. Its definition in physics is presented as a long-term indicator. Time through distance and speed is calculated by the formula t = S / V. Standard decoding:
S is the distance;
V – final speed (kilometer value);
t is time.
When speed is measured in km / h, time is also expressed in hours. In any system, events develop simultaneously.
Solving problems
It is possible to understand the action of time formulas with uniform motion or uniformly accelerated motion by solving the problem. Many sites offer an online calculator for easy counting. It is enough to enter basic data in the corresponding columns, after which the program will calculate everything on its own.
Problem 1.
The car was traveling at a speed of 200 km / h and drove only 80 km. It is required to determine the travel time of the car. Legend:
V is the speed;
S is the distance;
t is time.
Indicators must be converted from kilometers to meters, from hours to seconds: 1 km = 1,000 meters, 1 hour = 3600 seconds. We get S = 80,000 m, V = 200,000/3600 = 55.55 m / s. We find the speed by the formula: V = S / t = 80,000 / 55.55 = 1440.14 sec.
Solving problems
t = 1440
14/3600 = 0.4 hours.
Answer: the car will pass 0.4 hours.
With an uneven movement, the path traversed by the body is equal to the product of the average speed and the time during which the body moved.
Problem 2.
The movement of a point is given by the equation: x = 2t – 0.03t2. It is necessary to determine in what period the speed of the approach point will be equal to the zero mark. The coefficients are equal to 2m / s, 0.03 m / s2.
The problem conditions contain the function x (t). The speed can be calculated according to the formula V = dx / dt = 2 – 0.06t. We equate the speed to 0, we find t:
2 – 0.06t = 0
t = 2 / 0.06 = 33.33 sec.
It is necessary to determine the dependence of the acceleration module on time: A (t) = dv / dt = -0.06.
Problem 3.
The plane gains 350 km / h for takeoff. Acceleration time must be determined if speed is reached at the end of a 2 km runway. The movement is considered uniformly accelerated.
With uniformly accelerated motion, the formula looks like S = V0t + at2 / 2. In this case, V = V0 + at. The acceleration of the aircraft begins from a state of rest, that is, V0 = 0.
S = at2 / 2
V = at.
S = (V / t) * (t2 / 2) = Vt / 2.
S = 2000 m
V = 350 km / h = 97.2 m / s.
t = 2S / V = 2 * 2000 / 97.2 = 41.15.
Thanks to the calculation, it is known that the acceleration of the aircraft lasts 41.15 seconds.
