When the driver of an automobile applies the brakes, the...

Name: Problem 139, Chapter 5: Chemistry A Molecular Approach
Uploaded: 2019-11-10T13:49:49-08:00
Duration: 41 s
Channel: Sisi Gao
Description: When the driver of an automobile applies the brakes, the passengers are pushed toward the front of the car, but a helium balloon is pushed toward the back of the car. Upon forward acceleration, the passengers are pushed toward the back of the car, but the helium balloon is pushed toward the front of the car. Why?

When the driver of an automobile applies the brakes, the passengers are pushed toward the front of the car, but a helium balloon is pushed toward the back of the car. Upon forward acceleration, the passengers are pushed toward the back of the car, but the helium balloon is pushed toward the front of the car. Why?

Key Concepts

Non-Inertial Reference Frames and Fictitious Forces

When a vehicle accelerates or decelerates, it creates a non-inertial reference frame where fictitious forces appear to act on objects within the vehicle. These apparent forces, such as the backward 'force' felt by passengers during acceleration or the forward push during braking, arise because of the vehicle's acceleration, altering the apparent motion of objects inside.

Buoyancy in Accelerating Fluids

Buoyancy in accelerating fluids explains the counterintuitive behavior of the helium balloon. As the car changes speed, the air inside it is slightly compressed in the direction opposite to the acceleration. The balloon, being less dense than the surrounding air, is pushed in the opposite direction to where the air accumulates, causing it to move in a direction that is seemingly opposite to the motion of other objects in the car.

Inertia

Inertia is the tendency of objects to resist changes in their state of motion. In the context of a moving vehicle, this means that passengers, which are much denser than the surrounding air, continue moving at their original speed or direction until a force (such as braking or accelerating) causes a change in their motion. This is due to Newton's first law of motion, which states that an object in motion stays in motion unless acted upon by an external force.

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