Question

Use ideas of momentum to explain how seat belts reduce the risk of injury during a collision

Some people agree that wearing seat belts reduces the risk of injury to people in the car. However, they say that the risk to other road users might be increased. Suggest why it would be difficult scientifically to test this suggestion.

Answer 1

all this is the fault of "inertia"....

Answer 2

@paki huh?

Answer 3

yeah keep in view the concept of inertia, and you will see the magic of seat belts....

Answer 4

when a moving car stops quickly, the passengers move forward towards the windshield . Seat belts change the forces of motion and prevent the passengers from moving. Thus the chance of injury is greatly reduced . That's what I know :D

Answer 5

@paki Thanks :) @sarah786 Oooh thank you ever so much!! :)

@emcrazy14 could you help with the last bit of the question? :)

Answer 6

My pleasure :D ^_^

Answer 7

According to Newton's first law, an object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. It is the natural tendency of objects to keep on doing what they're doing. All objects resist changes in their state of motion. In the absence of an unbalanced force, an object in motion will maintain its state of motion. This is often called the law of inertia.

The law of inertia is most commonly experienced when riding in cars and trucks. In fact, the tendency of moving objects to continue in motion is a common cause of a variety of transportation injuries - of both small and large magnitudes. Consider for instance the unfortunate collision of a car with a wall. Upon contact with the wall, an unbalanced force acts upon the car to abruptly decelerate it to rest. Any passengers in the car will also be decelerated to rest if they are strapped to the car by seat belts. Being strapped tightly to the car, the passengers share the same state of motion as the car. As the car accelerates, the passengers accelerate with it; as the car decelerates, the passengers decelerate with it; and as the car maintains a constant speed, the passengers maintain a constant speed as well..... @YasmeenaK

Answer 8

pleasure @YasmeenaK

Answer 9

hope it will be clear to you now....

Answer 10

@paki hmm.. I get what you mean, but we're not studying about inertia so we can't use it in the answer :/
@AccessDenied Could you help, if you don't mind?

Answer 11

idea of momentum is related with inertia....

Answer 12

When you are in a car crash, the car will come to a stop and the passenger will keep moving towards the windshield (due to inertia, the passenger's body wants to keep their state of motion).

First we can compare the impulse (change in momentum):

\[\Delta p = \Delta m _{f} \Delta v_{f} - \Delta m_{i} \Delta v_{i}\]

Well the passenger isn't changing their mass (unless they lose some limbs in the process!) and the velocity goes from a certain velocity to 0. So the impulse is the same for if you wear a seat belt or if you don't wear one.

But we can also write impulse as:

\[\Delta p=F \Delta t\]

Now we have the net force (F) and change in time (t) involved. So now that we know that the impulse is the same, lets determine what would happen to the passenger when they don't wear a seat belt and when they do wear one:

If the passenger was NOT wearing a seat belt, their body would come to a stop very QUICKLY as they hit the windshield or dashboard! So if time (t) is short, the force F is large (and that large force would hurt!)

By wearing a seat belt, we increase the time (t) it takes for the passenger to come to a complete stop. If t is increased, the the force (F) does not need to be as large, which will reduce injury to the person.



You can also think of it in terms of forces... A large force will be required to stop a person's velocity as they hit the windshield (momentum changes very quickly). A smaller force will be required to stop them if their momentum is changed more gradually over a longer period of time (with the seat belt).


And just one more example, if you throw a baseball straight up into the air and then catch it without moving your hand downwards, the impulse is acting over a very short time period, so there is a larger force needed to stop the ball and usually your hand will feel some pain.

But if you throw the baseball up to the same height as before and then as you catch it you move your hand down slightly while catching the ball, the impulse is still the same, but the time you took to stop the ball has INCREASED, and thus it required a SMALLER force, so your hand doesn't hurt as much!

As for the last part of your question, I am not quite sure... Perhaps people will drive more recklessly when they know that they are protected by a seat belt and so they will be a greater risk to other road users?