Why Do We Appear to Lean Left on a Curved Bus Ride?

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Discussion Overview

The discussion revolves around the phenomenon of why passengers appear to lean left when a bus moves along a curved road to the right. It explores concepts related to inertia, forces experienced during acceleration, and the perception of motion within a turning vehicle.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that the body's instinctive response to resist external forces causes individuals to lean into the turn, countering the perceived outward pull due to inertia.
  • Others propose that the principle of equivalence implies that the acceleration felt in the bus can be likened to a pseudo force of gravity acting in the opposite direction.
  • One participant describes the effect of friction from the seat pushing the lower body while the upper body is swung around, contributing to the sensation of leaning.
  • Another viewpoint discusses the relationship between velocity changes and leaning, comparing it to pressing brakes in a car.
  • Some participants express confusion about the direction of leaning, with discussions about whether leaning left or right is necessary to avoid falling out of the seat.
  • There are claims regarding the sensation of force during acceleration, with references to free fall and gravitational effects, leading to disagreements about the nature of acceleration and force perception.
  • One participant mentions the role of the inner ear in balance and how it might influence the leaning behavior during the turn.
  • Several participants engage in a debate about the definitions and implications of acceleration, inertia, and the forces experienced in different contexts, including free fall.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the reasons for leaning left during a right turn, with multiple competing views and interpretations of the underlying physics and sensations involved.

Contextual Notes

The discussion includes various assumptions about forces, inertia, and the perception of motion, with some participants challenging the definitions and implications of acceleration and force in different scenarios.

Who May Find This Useful

This discussion may be of interest to those studying physics, particularly concepts related to motion, forces, and the effects of acceleration on the human body.

sphyics
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Why do we lean towards left when the bus moves along a curved road to right.
 
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sphyics said:
Why do we lean towards left when the bus moves along a curved road to right.

Because your body has a natural instinctive response to resist external forces to stay upright and keep the vision-plane level. When you go around a corner in a moving bus, your body's inertia tends to keep it going straight in accord with the Newton's first law. However, since you are inside the turning bus, it doesn't feel to you as if you are just going straight, it feels like you are being pulled toward the outside wall of the bus as it goes around the turn. This apparent "force" is what you are working against when you lean "into" the turn.
 
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According to the principle of equivalence gravity is indisdinguishable from acceleration. It means that inside a closed box you can not make an experiment that discerns gravity from acceleration.
Since the acceleration is to the right, we might just think of it as being attracted by a pseudo force of gravity to the left.
 
Interesting.
 
You can also think of it as the vehicle is pushing you to the right via friction (from the seat) but not directly pushing yout head, so your upper body is kind of being swung around by your point of contact.
 
You are reducing your velocity in your original direction as you transfer it to the new direction. When you lean to the left you are leaning in your original direction, same as when you press the brakes on your car and it pushes you forward.
 
When the entire world moves to the right and you stay in place, to you, it seems that the world stayed in place and you moved to the left.
 
When the entire world moves to the right and you stay in place
What makes you think this is the absolute way to see the situation?
 
The question is why do you feel a force when you accelerate. This is what you are doing when you are adding velocity to an orthogonal basis vector. The vehicle is changing it's relative velocity and so the seat grabs your bum and pulls you along with it. The fact that you feel a force in the opposite direction of acceleration agrees perfectly with the conservation of energy.
 
  • #10
sphyics said:
Why do we lean towards left when the bus moves along a curved road to right.

To keep from falling over...
 
  • #11
Lsos said:
To keep from falling over...

You would need to lean to the right to keep from falling over...
 
  • #12
LostConjugate said:
You would need to lean to the right to keep from falling over...

I had to think about it, but you're right. If you leaned to the left, wouldn't you fall outta your seat?
 
  • #13
thecow99 said:
I had to think about it, but you're right. If you leaned to the left, wouldn't you fall outta your seat?

Yup, that's why when you are in a vehicle that accelerates too fast you might fall over.
 
  • #14
LostConjugate said:
You would need to lean to the right to keep from falling over...

I didn't even think about that...so I guess the answer to the original question is, that you don't.
 
  • #15
The question is why do you feel a force when you accelerate
Not always. Consider free fall under gravity. You don't feel any force.
You will feel it, if its not a volume force(a beautiful term I saw in the Fundamentals Of Physics book by Resnick, Halliday).
 
  • #16
sganesh88 said:
Not always. Consider free fall under gravity. You don't feel any force.
You will feel it, if its not a volume force(a beautiful term I saw in the Fundamentals Of Physics book by Resnick, Halliday).

You are not accelerating in free fall however. You are only accelerating when you are on the ground.

You always feel a force when you are accelerating. General Relativity 101.
 
  • #17
Because the little bubble in your inner ear shifts to the left and it tells your body to shift to the left to keep the bubble centered.
 
  • #18
vibjwb said:
Because the little bubble in your inner ear shifts to the left and it tells your body to shift to the left to keep the bubble centered.

Nah, test dummies also lean to the left.

Helium balloons lean to the right, now there is food for thought.
 
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  • #19
LostConjugate said:
You are not accelerating in free fall however. You are only accelerating when you are on the ground.
What? Care to explain what you have posted?
 
  • #20
sganesh88 said:
What? Care to explain what you have posted?

You are not accelerating in free fall.

The air around you is accelerating, because the air is touching the ground. The buildings around you are accelerating, because they are on the ground.

When you are in a gravitational field you accelerate at the rate g in the direction opposite the mass. Where g is the gravitational acceleration, about 9.8 near earth.

If you are in free fall you are falling with acceleration equal to the gravitational acceleration g in the direction of the mass. 9.8 - 9.8 = 0
 
  • #21
LastConjugate said:
You are not accelerating in free fall.

http://en.wikipedia.org/wiki/Free_fall" article on free fall.
Near the surface of the Earth, an object in free fall in a vacuum will accelerate at approximately 9.8 m/s2, independent of its mass

You better understand what is acceleration first.
 
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  • #22
It is not taking into account the cancellation of gravity. You always feel a force when undergoing acceleration.

F = ma

Mass resists acceleration, we have mass, so we feel this resistance.

The Earth is accelerating.
 
  • #23
It is not taking into account the cancellation of gravity
Gravity isn't getting canceled here. A mass m under free fall near Earth is subjected to a force of mg.
 
  • #24
Mass resists acceleration, we have mass, so we feel this resistance.
Mass per se does not *resist* acceleration. However huge an object might be and however negligible a force might be, the object will suffer a non-zero infinitesimal acceleration.
Its a little like filling a container. Have one with a huge base? a given quantity of water will produce only a small increase in level. Small base? The same quantity of water will produce a significant increase in level. That doesn't mean the base factor is *resisting* the water filling process. There will inevitably be an increase in level, however small.
 
  • #25
sganesh88 said:
Mass per se does not *resist* acceleration. However huge an object might be and however negligible a force might be, the object will suffer a non-zero infinitesimal acceleration.
Its a little like filling a container. Have one with a huge base? a given quantity of water will produce only a small increase in level. Small base? The same quantity of water will produce a significant increase in level. That doesn't mean the base factor is *resisting* the water filling process. There will inevitably be an increase in level, however small.

Correct, though resistance is a good word for explaining the effect. A larger base resists the rise of the water level.

If the water level is not rising, your not adding any water. Since your organs are not pressed against your lungs you are not accelerating downward.
 
  • #26
LostConjugate said:
A larger base resists the rise of the water level.
It rather *damps* the increase in the level.

Since your organs are not pressed against your lungs you are not accelerating downward.
This isn't a logical statement. The definition of acceleration doesn't include constraints of organs pressing against our lungs.
 
  • #27
SpectraCat said:
Because your body has a natural instinctive response to resist external forces to stay upright and keep the vision-plane level. ...

This apparent "force" is what you are working against when you lean "into" the turn.

Lsos said:
I didn't even think about that...so I guess the answer to the original question is, that you don't.

Guys, guys, guys. The OP does not mean "why do we deliberately lean to the left", he means "why do we fall to the left".

i.e. When a bus goes to the right, your body will appear to fall to the left. (It is simply inertia.)
 
  • #28
I am with Dave on this. You do not lean left, you keep going straight while the bus turns. Thus appearing to make you lean away from the turn.
 

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