Science Forums

# Speed of Earth and how we remain on Earth.

## Recommended Posts

Question:

The Earth is travelling at a speed of about 15miles/sec (aproximately). Let's consider an example: we throw a baseball high up in the air and the ball falls back after 5 seconds. But by this time the Earth would have travelled 75 miles (15 x 5 = 75) and the ball would have landed in a place 75 miles from where we would have initially thrown the ball from. But apparently that does not happen.

What am I missing?

Thanks for everyone's input.

Regards-

AMT.

##### Share on other sites

this is just like when you throw a ball out of a moving car.

car 50mph

ball 40mph

ball now traveling 90mph

earths spin DOES affect the balls movement when you throw it up, but it's very very small.

when a space shuttle takes off, it's actually going straight up but since earth is spinning it's smoke path looks curved.

##### Share on other sites

sorry i can't be more ellaborate, i'm more of a listener.

##### Share on other sites

Thanks.

But I was referring to the linear velocity of the Earth it self, not the angular velocity of its spin. The Earth itself is travelling through space at a speed of about 15 miles/sec right?

In the case of the car, it's assumed that we are throwing the ball in the direction of the car's directional velocity. So this way we can add both the velocities together.

Now let's take the example of the car again: In case we throw the ball upwards when the car is travelling, then the ball is surely going to fall behing us...OR would it not? :naughty:

I was applying the same rule to the Earth instead of the car.

What am I missing?

AMT-

##### Share on other sites

if there was no air resistance, the ball would just go up, come down, and land back in your hand.

but since there's air resistance, the ball would be pushed behind.

##### Share on other sites

The Earth itself is travelling through space at a speed of about 15 miles/sec right?

And the Earth's atmosphere is travelling through space with it, right?

##### Share on other sites

I'm not sure if my explanation is correct:

If the Earth is travelling at 15 miles/hour, then we are also traveling at 15 miles/hour in space, right?

So basically, 15miles/hour is the horizontal velocity. When we throw the ball up in the air, we are giving it some vertical velocity. The total velocity of the ball is the vector sum of the vertical and horizontal velocity, which is 15 miles/hour. The horizontal velocity is remains the same because it is not affected by gravity. Therefore the balls travels horizontally just as much as we travel in space, so it makes it seems like the ball is moving straight up and straight down.

##### Share on other sites

The Earth travels at a fascinating 15 miles/second.

Let's analyze this example: We are travelling in a BMW convertible at 100 MPH. Someone in the back seat throws the ball straight up. I agree that since we are throwing the ball while in motion, we would have both horizontal and vertical component vectors. Now let's ignore the air resistance etc. Do you think after about 5 seconds, the ball would still fall insider the speeding BMW?

What if we were travelling in a plane at 1000MPH and did the same thing? I am sure there should be a speed threshold at which we will NOT be able to catch the ball, right?

AMT-

##### Share on other sites

why would there be?

##### Share on other sites

I'm not sure if my explanation is correct:
Your explanation is quite correct Aki!!! :naughty:

It is really the principle of relativity. One can find a discussion of it in Galileo's dialogue, arguing against those who thought the Earth must be still simply because we don't feel that it's moving.

##### Share on other sites

I am sure there should be a speed threshold at which we will NOT be able to catch the ball, right?

Like Orb asks, "why"? There is no reason for there to be a speed threshold. The only arguably valid point here would be that there are limits to how fast we can travel and still stay within Earth's atmosphere.

##### Share on other sites

The only real limit to traveling is the speed of light, obviously (well, obviously, only after having dove into relativity without comming up for air until you understand it. That could mean reading it 3 or 4 times (both the special and general versions). Or it may nver be obvious.

Point: Light speed is the limit for a particle with no mass, e.g., a photon. But mass could get no where near the speed of light.

Galaxies at the visual horizon only appear to racing away precisely at the speed. Relative though my dear Watson.

I read all the time about there being no restframe in the universe, or absolute space as it is often called. Because it brings back memories of the old Newtonian space, or because it is reminicent of the eather, fixed stars, static universe models, Olbers paradox, Minkowski spacetime, or lambda.

So my question to those who say we are traveling at such and such a velocity is: compared to what?

PS this is not a trick question, and I already know the answer to it. I just want to keep you guys and girls on your toes...

A.M. aka Coldcreation

##### Share on other sites

I think I am getting this thing down, but trying to get a better understanding.

Here is another example: After throwing the ball from a moving Ferrari travelling at 100MPH, the car suddenly accelerates to 300MPH. Now would not there be a difference when the ball falls back? Now our angles would have changed. i.e; the triangle formed by the angles of the balls ascent and descent.....

AMT

##### Share on other sites

So my question to those who say we are traveling at such and such a velocity is: compared to what?

Please do not hijack topics by posing questions that are unrelated to the issue. This is a good question for a new topic (although it has been discussed at length before).

##### Share on other sites

Here is another example: After throwing the ball from a moving Ferrari travelling at 100MPH, the car suddenly accelerates to 300MPH. Now would not there be a difference when the ball falls back?

Yes, and this is rather intuitive, really. When the car accelerates it will have a larger speed than the ball.

##### Share on other sites

The Earth travels at a fascinating 15 miles/second.

Let's analyze this example: We are travelling in a BMW convertible at 100 MPH. Someone in the back seat throws the ball straight up. I agree that since we are throwing the ball while in motion, we would have both horizontal and vertical component vectors. Now let's ignore the air resistance etc. Do you think after about 5 seconds, the ball would still fall insider the speeding BMW?

What if we were travelling in a plane at 1000MPH and did the same thing? I am sure there should be a speed threshold at which we will NOT be able to catch the ball, right?

AMT-

No, the ball wouldn't fall in the BMW. Here are some examples that may help.

We are on the Earth as it is traveling 15 miles/second as is it's atmosphere. Imagine that you are inside a closed moving vehicle with some headroom like a bus. Iamgine that it has a sunroof as well, but it is closed for now.

As you are sitting there holding the ball, you, the ball and the air around you are all moving together so your velocity relative to each other is 0. As you toss the ball into the air you impart a vertical velocity to it but it still has the horizontal velocity that you and the air around you have. The horizontal velocity of the air relative to the ball is still 0 so it doesn't impart any additional deflective energy to the ball. As you and the ball and the air move together in the bus the ball falls back to your hand.

Now imagine it is a still day to eliminate the wind for ease of discussion. As the bus is traveling it has velocity relative to the air it is moving through. To someone inside the bus the point of view is one that the air outside the bus is blowing at the bus' velocity. If you open the sunroof and stick your hand out the still air will push against it with the velocity that the bus is moving at. If you toss the ball up through the sunroof it will feel the same effect and the air will push it of course.

All in all you have to consider the relative velocity of all of the parts of the equation.

##### Share on other sites

Thanks everyone for your valuable insight.

I think I have the sucker down now ;)

## Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.