Question

Examples for 1stlaw motion,2,3,eg for inertia

Answer 1

The detailed explanation is as follows.

What are some examples of Newton's First Law of Motion?
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Joe Redish, Researcher in physics education and teacher of physics for 45 years.
Answered Aug 3
Here are three characteristic examples.
A large box is sitting on the floor and you want to move it from one side of the room to the other.
A freight train is coming down the track at 50 miles/hour and you are deciding whether to try to sneak across the level crossing.
You are swimming through water at an (approximately) constant velocity.
In the first case, we know intuitively (and correctly) that we need to exert a force (a push or a pull) on the crate in order to get it moving. In the second case we know (we better know!) that the train is going to be very hard to stop. It is going to keep going very fast unless the driver slams on the brakes — and even if that is done, the train will tend to keep going. Finally, in the third case, you know you have to keep swimming or you will come to a stop.
How do we reconcile these ideas — that something that is at rest will stay at rest unless there is something acting on it and that something that is moving will keep moving unless something acts on it — except what about 3?
The resolution is in the combination of Newton’s first and second laws. The first law says that an object will maintain whatever velocity it has unless an UNBALANCED FORCE acts on it. Newton’s second law tells us how that unbalanced force changes the object’s velocity.
I’ve emphasized “UNBALANCED” here, because one of the biggest problems students have with Newton’s laws is confusing the forces they are exerting with the net force — the sum of all the forces acting.
In the first case, there are no (horizontal) forces acting on the box. To change its speed, you have to exert a stronger force than the friction the floor is exerting on the box to speed it up. But once you have it moving at a constant speed, you only have to balance the friction, not overcome it.
In the second case, the train is moving fast and would need forces on it to slow it down. When the brakes lock the wheels, there is friction between the wheel sliding on the rail and the rail that slows it down — but it’s not big enough to slow it down very fast.
In the third case, as you are moving through the water, you feel a frictional drag (viscosity) that would tend to slow you down. You have to pull on the water so it exerts a force back on you (Newton’s 3rd law) in order to keep your velocity from changing. As in the case of the box, to keep moving at a constant speed you only have to balance the friction so your velocity doesn’t change.

Taking a Look at Inertia Examples
One's body movement to the side when a car makes a sharp turn.
Tightening of seat belts in a car when it stops quickly.
A ball rolling down a hill will continue to roll unless friction or another force stops it.
Men in space find it more difficult to stop moving because of a lack of gravity acting against them.
If pulled quickly, a tablecloth can be removed from underneath of dishes. The dishes have the tendency to remain still as long as the friction from the movement of the tablecloth is not too great.
Shaking a bottle of ketchup. When bringing the bottom down, the suddenly stopping it, inertia is what causes the ketchup to come out of the bottle.
When playing football, a player is tackled and his head hits the ground. The impact stops his skull, but his brain continues to move and hit the inside of his skull. His brain is showing inertia.
If one drove a car directly into a brick wall, the car would stop because of the force exerted upon it by the wall. However, the driver requires a force to stop his body from moving, such as a seatbelt, otherwise inertia will cause his body to continue moving at the original speed until his body is acted upon by some force.

Hope it answers your question.
All the best!