6.1 Introduction to Constant Acceleration Motion
Constant acceleration is an important concept in physics that describes the motion of an object that experiences a steady (unchanging) increase or decrease in velocity over time. This type of motion is also known as uniformly accelerated motion, as the object’s velocity changes by a constant amount during each equal time interval.
One of the key properties of constant acceleration is that it produces a linear relationship between an object’s velocity and time. This corresponds to a quadratic (parabolic) relation between position and time.
As mentioned in the previous chapter, physics is all about understanding the physical conditions at play. Thus, when writing down the equations in this chapter, be sure to keep in mind the primary condition here. That is, these equations are valid for situations in which there is constant acceleration. In other words, the acceleration of the object does not change with time.
6.2 Constant Acceleration Equations
The following kinematic equations are essential when solving problems involving constant acceleration.
Note that the third equation says nothing about the time of motion This can be extremely useful when solving problems that don’t provide any information about the time during which the motion takes place.
6.3 Acceleration Due to Gravity
When discussing constant acceleration, we always start with acceleration due to gravity which is a crucial and intuitive example of this type of motion. Acceleration due to gravity is the rate at which objects fall toward the Earth due to the pull of gravity. This type of acceleration is a constant that affects all objects on earth, regardless of their mass or size.
The conventional standard for the acceleration due to gravity is given as:
However, this value will vary slightly depending on one’s location on Earth. Thus, most physicists will simplify the value to or even depending on the accuracy needed. This expression represents the change in velocity per second that an object will experience as it falls toward the Earth. It is important to understand that Earth is not special in this concept of acceleration due to gravity. Objects on other planets experience gravity as well. The acceleration due to gravity takes on a different constant value for each of the celestial objects below:
- Mercury:
- Venus:
- Earth’s Moon:
- Mars:
- Jupiter:
- Saturn:
- Uranus:
- Neptune:
- Pluto:
Please note that these values may vary slightly based on the specific location on each planet, but they provide a good general estimate.
It is also important to note that acceleration due to gravity only acts in one direction: downward. This means that objects will fall towards the earth with a constant acceleration of , unless acted upon by another force, such as air resistance.
The concept of acceleration due to gravity is crucial in understanding a wide range of physical phenomena, including projectile motion which we will study in chapter 11. By understanding acceleration due to gravity, we can make predictions about the motion of objects in projectile motion problems.
6.4 The Myth of Zero Gravity
Contrary to popular belief, astronauts do not experience “zero gravity.” Instead, they are in a state of weightlessness, which is caused by being in a state of free fall toward the planet they are orbiting. Although they appear to float, they are actually being pulled toward the planet by its gravitational field. Astronauts aboard the International Space Station, for example, are falling toward the Earth at a rate of which is the same rate at which objects fall to Earth’s surface due to its gravitational pull. However, because they are continuously falling, they do not hit the surface, and instead continue to orbit the planet. This continuous state of free fall gives the illusion of being weightless, but the astronauts are still being influenced by the gravitational field of the planet.
Acceleration due to gravity is a fundamental concept in physics that helps us understand how objects fall towards the earth and the motion of projectiles. It provides us with the tools to make predictions about the motion of objects and to solve a wide range of problems in physics.
Chapter Summary
This chapter looked into the concept of constant acceleration, describing the motion of an object whose velocity steadily increases or decreases over time. This uniformly accelerated motion results in a linear relationship between velocity and time and a quadratic relationship between position and time. We discussed the case of acceleration due to gravity which affects all objects on Earth. This principle extends to other celestial bodies, each having its own unique gravitational acceleration. Interestingly, astronauts in orbit experience continuous free fall rather than zero gravity, creating the illusion of weightlessness. We also introduced kinematic equations to calculate the position, velocity, and change in position of an object experiencing constant acceleration.
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