# Person in a bus (accelerating system)

• pinsky
In summary, the bus starts accelerating due to the force of friction between the bus and the person, which in turn results in a reaction force of the same magnitude but opposite direction on the person.

#### pinsky

Hy

I'm having some issues about the Newtons third law.

The image should represent a person in a bus with and the forces acting on them.
The bus and the person are observed from outside the bus. The bus starts accelerating because of the force $F_{BUS MOVING}$. This force represent the resultant force of the friction between the bus and the ground, and the buses starting force.

As a result, friction force $F_{P-BUS}$ occurs and it acts on the bus because of the mass of the person.
As a reaction, a force of the same size but opposite direction acts on the person $F_{BUS-P}$

What is the sum of the forces on the bus?
$F_{BUS MOVING}-F_{P-BUS}$ ?

How would one calculate $F_{P-BUS}$ by knowing the mass of the person and $\mu$?

Is this the solution?
$F_{BUS MOVING}-F_{P-BUS}=F_{BUS-P}$

Since in this case, the bus and the person have the same value and orientation. That is what a observer from the street would see, right?

#### Attachments

• person_in_bus.gif
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• trenje.gif
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Last edited:
Welcome to PF!

Hi pinsky! Welcome to PF!

(try using the X2 tag just above the Reply box )

FP-BUS always equals (minus) FBUS-P.

If you regard the friction as an internal force, then you ignore it, and F = (MBUS + m)a.

If you regard the friction as an external force, then you include it, and F - FP-BUS = MBUSa.

Thanks for the welcome.

I didn't understand your explanation though.

Could you perhaps draw all the forces in a situation where the bus is starting, and the friction between the bus and the person in the bus isn't enough to prevent the person from gently sliding. So in that case we can't observe the bus and the person as a single object.
Draw the forces as they appear from the point of view of a person standing still outside the bus.

I made you a template to spare the time :)

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• person_in_bus_template.gif
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I'm not drawing it, but if the force on the bus is F, and the friction force is G, then

F - G = MBUSaBUS,

G = mPaP

## What is a person in a bus accelerating system?

A person in a bus accelerating system refers to the physical laws and principles that govern the movement of a person inside a bus as it accelerates. It involves the study of forces, motion, and energy to understand how the person's body responds to changes in acceleration.

## What factors affect a person's experience in a bus accelerating system?

Several factors can affect a person's experience in a bus accelerating system, including the magnitude and direction of the acceleration, the mass and size of the person, and the seat design and materials. Other factors include the friction between the person and the seat, the person's body position, and any external forces acting on the person.

## How does a person's body respond to acceleration in a bus?

When a bus accelerates, the person's body experiences a force in the direction of the acceleration, causing them to move forward. This force is countered by the seat, which applies an equal and opposite force on the person's body. The person's body also experiences a change in velocity, which can cause discomfort or motion sickness.

## What are the safety considerations for a person in a bus accelerating system?

The design of the bus and its components, such as the seats and seat belts, play a crucial role in ensuring the safety of a person in an accelerating bus. It is essential to consider factors such as the bus's maximum acceleration, the force exerted on the person, and the potential for injuries during sudden stops or collisions.

## How is the study of a person in a bus accelerating system relevant in real-life situations?

The study of a person in a bus accelerating system has practical applications in various fields, such as transportation and sports. Understanding how a person's body responds to acceleration is crucial in designing comfortable and safe vehicles. It also helps in developing training programs for athletes to improve their performance and prevent injuries during high-speed movements.