This post will take a look at distance and displacement—two core ideas in classical physics.

To understand concepts such as distance and displacement, you first need to understand position. Position is the location of an object. When we are speaking of distance and displacement, this involves an object changing position. However, an object can only change position if it is relative to something else. For example, if a person walks 5 meters from their bedroom to the kitchen, this distance can only exist because there are two positions

• The bedroom
• The kitchen

The position of the person is defined by what we call a reference frame. The reference frame is a stationary object from which position is determined. In the example above, there are three positions

• The bedroom
• The kitchen
• The walking person

The bedroom is the reference frame. In other words, wherever the walking person goes, their position is measured in relation to the bedroom. The kitchen is simply the goal destination or where the walking person is going.

Distance

Distance is a measure of the length of the path between a person’s initial and final position. In our walking example, the person traveled 5 meters from the bedroom to the kitchen. This 5 meters is the distance.

bedroom walk 5 meters to the kitchen

Displacement is a little more complicated. Displacement is the net change in position. In other words, displacement compares your final position to your initial position and determines if there is a difference in these values. For example, if we use the walking example again, the displacement is the same as the distance. This is because the person walked 5 meters and did not move anymore. Doing some simple math, we can calculate the displacement as shown below

Final position – original position = displacement

5 – 0 = 5

The person traveled 5 meters to the final position of the kitchen. The original position is 0 meters because the bedroom is where the person started at and is the reference frame.

The value of the distance and the displacement are not always the same. For example, if the walking person goes to the kitchen and then returns to the bedroom, we get the following numbers

bedroom walk 5 meters to the kitchen

Kitchen walk 5 meters to the bedroom

The distance travel here is 10 meters as we went 5 meters to the kitchen and 5 meters back to the bedroom. However, the displacement is zero because our final position and our initial position are the same in that we left the bedroom and came back to the bedroom. There was a change in the distance but not in the person’s position when the walking was over.

Scalar and Vector

Distance is a measure of magnitude (amount of) length. In this situation, only the magnitude is being measured, so this is a scalar quantity. In the example above, the person walked 5 meters. We know the direction, but this is not needed to understand that the person walked 5 meters

Displacement is a measure of magnitude and also direction. When magnitude and direction are considered, it is called a vector quantity. In our example above, the person walked to the kitchen and then walked backed to the bedroom. Walking to the kitchen could be considered a positive distance while walking back to the bedroom would be regarded as a negative distance. This is why the displacement is zero in the second example. Walking back and forth essentially cancels the values out.

This examination of motion is called kinematics, which is the study of motion without being concerned with what causes this motion.

Conclusion

Distance and displacement are foundational concepts in physics on which many other complex ideas are built upon. Therefore, understanding how things move in relation to space is critical to appreciate for students studying this subject.

In this post, we will do a brief history lesson on the term natural philosophy and the branches of sciences that sprang from it. From there, we will look more closely at the world of physics

Natural philosophy was a catch-all term for the study of nature. Some of the fields associated with natural philosophy include biology, astronomy, and even medicine. With time, as knowledge grew, various subjects began to be spun off from natural philosophy into their own separate area of expertise.

For example, the subjects under natural philosophy have been divided into the natural sciences such as zoology and botany, and the physical sciences such as chemistry and physics.

Physics

The term physics comes from the Greek word “phusis,” which means nature. Therefore, physics is the study of nature or reality because nature is what many people consider to be real. Physics, in particular, has been further divided into classical and modern physics.

Classical physics covers the topics and discoveries of physics from the Renaissance until the end of the 19th century. As such, classical physics covers what the average person encounters in their day to day life and can be understood intuitively. The explanations that classical physics provide must fall under the following assumptions…

1. Matter must move at a speed less than 1% of the speed of light or about 3,000,000 meters per second.
2. The objects dealt with must be large enough to see with the naked eye.
3. Only weak gravity, like earth’s, can be involved.

Again, this is where life is for most of us. Classical physics must be understood before trying to understand modern physics. Modern physics throws out the three assumptions above with two main contributions, which are the theory of relativity and quantum mechanics.

Einstein’s theory of relativity states that the measured length of an object traveling at high speeds is shorter than an object at rest. By high speeds, we are talking about faster than 1% of the speed of light (this is breaking the first assumption mentioned above). For example, time, which is a measure of change, moves slower for an object traveling above 1% of the speed of light compared to an object at rest. This means that if you could travel this fast, you would age slower than someone at rest. Gravity can also affect time as satellites in space have to readjust their clocks to sync with the earth. This is called dilation.

Quantum mechanics deals with the very small, which is breaking the second assumption. We are talking about objects on the atomic and subatomic levels. The rules at this level are often bizarre because these tiny particles can travel almost the speed of light, thus breaking assumption 1. As such, this area of physics has its own distinct rules.

Conclusion

Natural philosophy is perhaps a term that many people are not familiar with. This is because the term has been chopped up and divided into many different branches of science. Within the sciences, even physics has several subdivisions as people continue to learn more about the world around them.