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Chapter 3: Problem 26

When involved in an automobile collision, a person not wearing a seat belt will move through the car and often strike the windshield directly. Which of Newton's laws explains why the person continues forward, even though the car stopped?

Short Answer

Expert verified
Newton's First Law of Motion explains why the person continues forward when the car stops.

Step by step solution

01

Identify the problem

Determine which of Newton's laws applies to the scenario where a person continues moving forward even after the car has stopped.
02

Consider Newton's First Law of Motion

Newton's First Law of Motion, also known as the Law of Inertia, states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.
03

Relate the law to the situation

In the context of the collision, the car stops suddenly due to an external force (the collision), but the person inside continues to move forward because there is no unbalanced force acting directly on them to stop their motion.
04

Conclusion

Therefore, the person's forward motion can be explained by Newton's First Law of Motion, which indicates that the person continues to move at the same velocity until an external force (such as the windshield) stops them.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Law of Inertia
Newton's First Law of Motion, also known as the Law of Inertia, explains why objects continue in their state of motion unless acted upon by an external force. This law can be simply stated as: an object at rest will stay at rest, and an object in motion will continue moving at a constant velocity unless it experiences an outside force. Let's break this down:

  • Inertia: The property of an object that resists changes to its state of motion. This means if an object is stationary, it won't start moving on its own, and if it’s moving, it won't stop or change direction unless something interacts with it.
  • Uniform Motion: This means moving in a straight line at a constant speed. There are no changes in direction or speed unless an external force comes into play.

In the case of an automobile collision, the car comes to a sudden stop due to an external force (the collision with another object). However, if a passenger is not wearing a seatbelt, their body will continue moving forward at the same speed the car was going before the collision, demonstrating the concept of inertia.
Automobile Collision Physics
Automobile collisions bring various physics principles into play, with Newton's First Law being central to understanding the aftermath for unrestrained passengers. Here's how:

  • Initial Motion: When a car is moving, everything inside it, including the passengers, is moving at the same speed.
  • Sudden Stop: When the car experiences a sudden stop due to a collision, it's the car that stops because an external force is applied to it.
  • Continued Motion: Because of inertia, a passenger without a seatbelt doesn't stop with the car but continues moving forward until another force (such as the windshield) stops them.

This continued motion often leads to injuries. Wearing a seatbelt provides the necessary external force required to decelerate the body at the same rate as the car, thus preventing the forward thrust into the car’s interior, and providing significant safety during a collision.
External Forces
Understanding the role of external forces is crucial in analyzing motion changes. These forces are responsible for changing the velocity of an object, whether it's coming to a stop, speeding up, or changing direction.

  • Definition: An external force is any force that originates from outside an object and acts upon it.
  • Examples: Gravity, friction, applied force (like a push or pull), and collision impact.

In the scenario of an automobile collision:
  • The car: The external force is the collision impact, which stops the car abruptly.
  • The passenger: Without an external force like a seatbelt to stop them, the passenger continues moving forward due to inertia, until they encounter another force (the dashboard or windshield).

External forces are necessary to alter the motion of objects, either to bring them to a rest, change their direction, or change their speed. In the absence of these forces, objects continue in their state of motion as per Newton's First Law of Motion.

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Most popular questions from this chapter

You are driving down a straight road at a speed of \(90 \mathrm{km} / \mathrm{h}\) and you see another car approaching you at a speed of \(110 \mathrm{km} / \mathrm{h}\) along the road. a. Relative to your own frame of reference, how fast is the other car approaching you? b. Relative to the other driver's frame of reference, how fast are you approaching the other driver's car?

An empirical science is one that is based on a. hypothesis. b. calculus. c. computer models. d. observed data.

When riding in a car, we can sense changes in speed or direction through the forces that the car applies on us. Do we wear seat belts in cars and airplanes to protect us from speed or from acceleration? Explain your answer.

A net force must be acting when an object a. accelerates. b. changes direction but not speed. c. changes speed but not direction. d. all of the above

Suppose you are pushing a small refrigerator of mass \(50 \mathrm{kg}\) on wheels. You push with a force of \(100 \mathrm{N}\) a. What is the refrigerator's acceleration? b. Assume the refrigerator starts at rest. How long will the refrigerator accelerate at this rate before it gets away from you (that is, before it is moving faster than you can run-of the order \(10 \mathrm{m} / \mathrm{s}\) )?
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