what is inertia.and how it works in day today life?

Answer 1

Inertia is a body's resistance to a change in velocity.
In day to day life it means that when you put something down like a book on a table, you would expect it to stay there unless it is moved by an external force (.e.g someone else, wind, earthquake). You would not expect it to spontaneously move around.

Answer 2

Momentum P = mv is a measure of inertia; where m is the rest mass of something and v is its velocity with respect to a non relativistic reference frame. And dP/dt = mdv/dt = ma = f = force, which is just a change in momentum over time (dP/dt).

Thus, v = constant so long as f = 0 and there is no acceleration (a). That is, due to inertia, momentum of inertial mass (m) will not change until a net force is applied. And, by the way, v = 0, when the body is at rest, is just a specific case of a constant velocity; so it suffices to say the a body will remain at a constant velocity until acted on by a net force.

Day to day inertia at work is difficult to find when P = mv = constant because there is almost always a net force f acting on whatever body there is unless, of course, it is standing still so that v = 0. Your car standing still in the driveway, for example, is an oh hum, boring example of inertia at work. There is no net horizontal force to get it rolling by overcoming the inertia at rest. In fact, anything just sitting there is an example of inertia at rest...but that is really boring. So let's look at things on the move, where v > 0.

You're doing 45 mph in a 25 mph school zone and a kid suddenly dashes out in front of your car. You slam on the brakes to slow to a stop before making that kid into a statistic. Can you stop in time? Well, that depends on your car's inertia as measured by its momentum P = mv.

You are looking for v = 0 so that P = mv = m0 = 0 when the car comes to a halt. So you need a deceleration (a) that gives v^2 = u^2 + 2aS = 0; where S = distance between your car and that kid when you slam on the brakes, u = 45 mph when you slam on the brakes, and a is that deceleration you need so that v = 0 before hitting the kid. Note that f/m = a; where f = kmg, the net force from braking, which is the friction force on the pavement from braking the tires.

Thus, 0 = u^2 + 2Sf/m = u^2 - 2Skmg/m = u^2 - 2Skg and solving for S = u^2/(2kg). So there you have it, when you plug in u, k, and g, you can determine if S is less than or greater than the distance between your car and the kid when you start to brake. But the fact that it takes some S of any length to bring the car to a halt is due to its inertia when the brakes were first applied.

In general, any time you accelerate or decelerate a force is required to overcome inertia (i.e., momentum). Just getting out of bed in the AM requires overcomiing your rest inertia in bed. You need to exert some force to get up.

Or, you're running down the hallway in school and your most admired professor suddenly comes around the corner in your path. To swerve around her, you need to exert a sideways force to change directions, and as velocity is a vector that means velocity is changed by that force. Or you need to exert a backward force to decelerate to a stop, like the kid and the car case.

So to answer your question inertia is a resistance to change in velocity and its measured by P = mv momentum. And it works in everything that has inertial rest mass m and velocity from 0 on up.

Answer 3

A body in motion tends to stay in motion in the same direction and speed. A body at rest tends to stay at rest.

Lots of things in day-to-day life. Think of simply driving a car around a curve. You can feel your body trying to move in a different direction than the car is turning. That is inertia working on your body. If the car is going too fast on a curve, inertia will force it off the road if the friction holding the tires to the road is overcome by the inertia.

If you are sitting down, you are a body at rest. When you stand up, the effort it takes is a combination of overcoming gravity and inertia.