# Relative Motion Comparing my motion vs an airplane

• Robloxian642
In summary: Velocity is the direction of motion.You're still a bit new to this material - maybe try reading some tutorials first?Be careful with 'speed' versus 'velocity'. Technically, speed is a magnitude, so never negative. Velocity is the direction of motion.
Robloxian642
Homework Statement
What would be my relative velocity be if I compared to myself sitting vs a airplane going 800km/h
Relevant Equations
im sitting plane moving
I'm having trouble understanding the plane one

This is what I understand so far v

I'm sitting at a chair right now and if I compare my relative motion to the ground my relative velocity would be 0m/s but if I compare my motion to the solar system I would be moving very fast. I just can't grasp my relative motion if I compare myself to a airplane

So if I compared myself to the airplane would my relative velocity be -800km/h

Robloxian642 said:
Homework Statement:: What would be my relative velocity be if I compared to myself sitting vs a airplane going 800km/h
Well, you haven't specified
1. where you're sitting, or
2. what reference point the plane is moving 800km/h relative to.

Robloxian642 said:
...if I compare my motion to the solar system I would be moving very fast..."
The solar system is not a discrete object. You can't really compare its motion without specifying a reference point.

Robloxian642 said:
So if I compared myself to the airplane would my relative velocity be -800km/h
Where does the minus symbol come from? You'd need to specify what direction the plane is going.All that aside, what exactly are you having trouble with?

If you are sitting in a chair on the ground (i.e. on Earth), can you even say how fast the aircraft is moving without specifying what that speed is relative to? (Hint: no, you can't.)

Robloxian642
Each one of those velocities that you mention can be considered vectors; therefore, any relative velocity should be the result of a vectorial addition, which will result in one vector velocity that has direction and magnitude.

Robloxian642
im still very new to this material I drew out a diagram on what I wanted to figure out. This is not a homework question just something out of curiosity

I just want a easier way to think of relative motion

Robloxian642 said:
im still very new to this material I drew out a diagram on what I wanted to figure out. This is not a homework question just something out of curiosity

I just want a easier way to think of relative motion

View attachment 273014
Clearly the plane is going at -800 km/h relative to the ground. See which way the man in the chair is facing? If he turned around, then the plane would be going +800 km/h.

Possibly it would help to get back to basics. Draw a coordinate system on the ground. Label it in kilometers. Figure out where the plane is at time zero. Figure out where the plane is at time time 10 seconds. Divide the difference in position by the difference in time. That is how velocity is defined.

Now repeat it for the plane. Draw a coordinate system anchored to the plane. Figure out where the man is at time zero according to that coordinate system. Figure out where the man is at time 10 seconds. Divide.

jbriggs444 said:
Clearly the plane is going at -800 km/h relative to the ground. See which way the man in the chair is facing? If he turned around, then the plane would be going +800 km/h.
Note that this is an implicit convention.

We all accept that positive velocity is defined in this diagram by the direction of the guy in the chair is facing. But there's no objective reason for it to be so.

Last edited:
jbriggs444
DaveC426913 said:
Not that this is an implicit convention.
"Note that ..."?

DaveC426913
Robloxian642 said:
im still very new to this material I drew out a diagram on what I wanted to figure out. This is not a homework question just something out of curiosity

I just want a easier way to think of relative motion

View attachment 273014
Be careful with 'speed' versus 'velocity'. Technically, speed is a magnitude, so never negative.

## 1. How does relative motion affect my perception of speed compared to that of an airplane?

Relative motion refers to the perceived motion of an object in relation to another object. In the case of comparing your motion to that of an airplane, your perception of speed may be affected by the distance between you and the airplane, as well as the direction and speed of the airplane's motion. For example, if you are standing on the ground and the airplane is flying overhead, you may perceive the airplane to be moving faster than you because it is covering a larger distance in a shorter amount of time.

## 2. What is the difference between absolute and relative motion?

Absolute motion refers to the actual, measurable motion of an object in space, while relative motion is the perceived motion of an object in relation to another object. Absolute motion can be measured using tools such as speedometers and radar, while relative motion is based on an observer's perception and can vary depending on the observer's location and perspective.

## 3. How does the concept of frame of reference play a role in relative motion?

Frame of reference is an important concept in relative motion as it determines the point from which an object's motion is observed and measured. For example, if you are standing on a moving train and observe a stationary object outside, your frame of reference is the train. This will affect your perception of the object's motion and speed compared to if you were standing on the ground.

## 4. Can relative motion be used to explain the concept of air resistance?

Yes, relative motion can help explain the concept of air resistance. Air resistance is the force that opposes the motion of an object through air. When an airplane is flying, it is experiencing air resistance as it moves through the air. However, from the perspective of someone on the airplane, it may appear as though the air is moving past them rather than the airplane moving through the air. This is an example of relative motion, where the frame of reference (the airplane) affects the perception of the motion of the air.

## 5. How can relative motion affect the accuracy of measurements?

Relative motion can affect the accuracy of measurements because it is based on an observer's perception and can vary depending on the observer's frame of reference. This means that two different observers may measure the same object's motion differently depending on their location and perspective. To ensure accurate measurements, it is important to establish a consistent frame of reference and consider the effects of relative motion on the measurement.

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