# Riddle me this...

#### Slavik

##### XenForo moderator
Staff member
You place a toy helicopter in a sealed lorry. Using accurate skills, you then cause the helicopter to hover inside the lorry but not changing its forward or sideways movements.

If the lorry were to start moving. Would the helicopter move with it, or would it slowly move towards the back of the lorry befor ehidding the doors?

To further confuse the issue. If you were inside a sealed lorry traveling at 70kph, and you got the helicopter to lift off perfectly vertical with no forwards or sideways movements, if the lorry sped up would it cause the helicopter to move backwards?

#### jonsidneyb

##### Well-known member
You place a toy helicopter in a sealed lorry. Using accurate skills, you then cause the helicopter to hover inside the lorry but not changing its forward or sideways movements.

If the lorry were to start moving. Would the helicopter move with it, or would it slowly move towards the back of the lorry befor ehidding the doors?

To further confuse the issue. If you were inside a sealed lorry traveling at 70kph, and you got the helicopter to lift off perfectly vertical with no forwards or sideways movements, if the lorry sped up would it cause the helicopter to move backwards?
It will move with the Lorry,

This is relativity.

If you are in an aircraft and drop a baseball it will fall straight down relative to the passengers in the plane but might show 500 mph to those on the ground. Now lets say we through the baseball forward over a chronograph inside the plane it is moving at 100 mph but measured from the ground it is 600 mph. We can add the speed of the earth moving around the Sun. We can add the movement of the Sun in the Milky Way. We can add the movement of the Milky Way in the Local Group. We can add the movement of the Local Group against something else.

Albert would be proud, you are dealing with the basics of Relativity.

#### Brogan

##### XenForo moderator
Staff member
Try jumping in the air next time you're on a plane flying at 1000 kph

#### Slavik

##### XenForo moderator
Staff member
Try jumping in the air next time you're on a plane flying at 1000 kph

#### Brogan

##### XenForo moderator
Staff member
Do you feel wind on your face when accelerating in a car?

#### Brandon Sheley

##### Well-known member
the answer to #1 is... the "lorry" which btw I have no idea what that is, but I'm guessing it's a car of some sorts, would move forward while the helecopter would stay still and thus look like it was moving back.
If you started flying the copter while you were moving already, it would continue in that movement.

Do you feel wind on your face when accelerating in a car?
You will if you don't have a windshield..

#### jonsidneyb

##### Well-known member
No it's not
I throw base ball in airplane moving at 500 mph relative to the ground from back to front at 100 mph relative to the plane I get this.

Relative to the passengers on the plane the ball is moving 100 mph, relative to the ground it is moving 500+100=600 mph.

Relative to the sun it is moving the speed of the earth plus the other motions.

This is a part of relativity.

#### jonsidneyb

##### Well-known member
the answer to #1 is... the "lorry" which btw I have no idea what that is, but I'm guessing it's a car of some sorts, would move forward while the helecopter would stay still and thus look like it was moving back.
If you started flying the copter while you were moving already, it would continue in that movement.

You will if you don't have a windshield..
Now you have an externality. The air outside is upsetting what is inside. They where not moving together since that air was not inside at the start of the movement..

#### jonsidneyb

##### Well-known member
You place a toy helicopter in a sealed lorry. Using accurate skills, you then cause the helicopter to hover inside the lorry but not changing its forward or sideways movements.

If the lorry were to start moving. Would the helicopter move with it, or would it slowly move towards the back of the lorry befor ehidding the doors?

To further confuse the issue. If you were inside a sealed lorry traveling at 70kph, and you got the helicopter to lift off perfectly vertical with no forwards or sideways movements, if the lorry sped up would it cause the helicopter to move backwards?

A new equilibrium has to be reached with changes in direction and velocity. At constant motion what I originally posted holds. During a change in direction or velocity you are subject to G-Forces that go away until a new equilibrium is met.

#### Slavik

##### XenForo moderator
Staff member
the answer to #1 is... the "lorry" which btw I have no idea what that is, but I'm guessing it's a car of some sorts, would move forward while the helecopter would stay still and thus look like it was moving back.
If you started flying the copter while you were moving already, it would continue in that movement.

You will if you don't have a windshield..
this is a lorry

To respond to your answer, by that logic, as the lorry moves forwards it would create a vacume as the air in the lorry would be "staying still" while the lorry moves forwards

#### Brogan

##### XenForo moderator
Staff member
You will if you don't have a windshield..
Which is why I said car and not motorbike...

#### jonsidneyb

##### Well-known member
At constant speed you can assume things inside will act as if you are not moving. When you change velocity or direction there will be a temporary G-Force effect that will go away yet you will not feel a change in the air due to pressure. Once the new velocity is established a new equilibrium occurs and then things operating inside the box will again behave as if the container is not moving.

#### RobParker

##### Well-known member
I throw base ball in airplane moving at 500 mph relative to the ground from back to front at 100 mph relative to the plane I get this.

Relative to the passengers on the plane the ball is moving 100 mph, relative to the ground it is moving 500+100=600 mph.

Relative to the sun it is moving the speed of the earth plus the other motions.

This is a part of relativity.
Yes, you right there but it's not the same problem.

The helicopter is not in contact with the lorry. As the lorry accelerates, it moves forward whilst the helicopter remains stationary. In the frame of reference of the lorry, the helicopter moves backwards (and hits the door). In the frame of reference of the earth, the lorry has moved and the helicopter has stayed stationary.

#### jonsidneyb

##### Well-known member
You place a toy helicopter in a sealed lorry. Using accurate skills, you then cause the helicopter to hover inside the lorry but not changing its forward or sideways movements.

If the lorry were to start moving. Would the helicopter move with it, or would it slowly move towards the back of the lorry befor ehidding the doors?

To further confuse the issue. If you were inside a sealed lorry traveling at 70kph, and you got the helicopter to lift off perfectly vertical with no forwards or sideways movements, if the lorry sped up would it cause the helicopter to move backwards?
I will answer the question properly now.

The speed of the lorry is not important in how the helicopter behaves, it will only be changes in velocity and direction, any constant speed will not have an effect.

When you are in a car and stomp the peddle hard you will be pushed into the seat but once you have settled on a particular velocity it will be as if you are not moving on the inside of the car. Any bumps in the road are like micro changes in direction.

#### jonsidneyb

##### Well-known member
Yes, you right there but it's not the same problem.

The helicopter is not in contact with the lorry. As the lorry accelerates, it moves forward whilst the helicopter remains stationary. In the frame of reference of the lorry, the helicopter moves backwards (and hits the door). In the frame of reference of the earth, the lorry has moved and the helicopter has stayed stationary.
I addressed this one in post 11

#### RobParker

##### Well-known member
The speed of the lorry is not important in how the helicopter behaves, it will only be changes in velocity and direction, any constant speed will not have an effect.
Correct. But the acceleration of the lorry is vital. If it "starts moving" as in the question, then it's accelerating.

#### jonsidneyb

##### Well-known member
Correct. But the acceleration of the lorry is vital. If it "starts moving" as in the question, then it's accelerating.
Yep, I realized that after I read all of the first post.

I just say speed of lorry and went straight to relativity. I went back and read what he actually posted and saw that there where changes in velocity.