Newton's First law
According to this law, an object at rest tend tend to stay at rest and an object in motion tend to stay in motion, with same speed in the same direction unless it is compelled by same external unbalanced force to change that satat. This law provides the qualitative definition of force.
Example of Newton's First law
The card and coin experiment
Take a smooth card and keep it on a glass. Place a coin on the card and flick sharply in the horizontal direction. The cord flies away and the coin drops into the glass.
Initially, there are tow forces on the coin. The earth pulls the coin downloads and the card pushes it upwards. The forces balance each other and the coin remains at rest.
When we apply a horizontal force on the card, it is accelerated and it moves away. Since the friction between the card and the coin is negligible there is no force on the coin in the horizontal direction. It remains in its original position due to inertia of rest.
When the card moves away from underneath the coin, the normal force on the weight is the only force on the coin becomes zero. The weight is the only force on the coin and hence, it accelerates downwards to fall into the glass.
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