Forces.... why?

Question

why is it that the term equal force is used if for example a cup is places on a table

the upward force on the table is said to be equal with the gravitational force of the cup.

now if you put a 1kg and a 10kg cup on a table how can the forces be the same to keep the both cups still... if the table is pushing up with the equal force on the 10kg cup, why doesnt the 1kg cup go flying into the air?

Answer 1

Good question. Understanding how force works seems easy sometimes but i think theres small details in what force realy means that makes it difficult to understand. Im still strugging with small details my self.

Your question, yeah its almost a miracle how force works. The gravitational force that an object feels will be differnt then the force that another object feels. That such a strange thing i think, but its the way it works....a piano will be pulled towards the earth with a stronger force than a penny, and the result will be that both objects have the same acceleration. You must try to see that it is the acceleration being constant that makes the situation make sense. Now, if there is a 1kg cup on the table then it will be pulled towards the earth with a 10N force. In order for the table not to break under the weight the bonding of the tables molecules must be strong enough to support the 10N force...no more / no less. If you put a10kg cup, then the bonding of the tables molecules must be strong enough to support the 100N force pressing on it...no more/no less. But if a 1000N force is on the table then a the table will not be able to support it and the cohesion of the table will be ripped apart. The table can only support so much weight.

Answer 2

because the reaction of the table will be equal to the amount of the force exsert by cup.
so if you but a 10 kg cup on the table, then the table will give a reaction of 10 kg only but in the oppesite direction.
and newton seconde law confir that as i"ll show:
Sumation of force for object in equilabium (stationary) F=0
so the cup will have a down word force of 10*g
and the table will have a reaction force = 10*g
and these tow equal force will cancel each other because they are oppsite in the direction.

Answer 3

In your example, the force of the table on the heavier cup is greater than its force on the lighter cup.

Answer 4

On a level surface, the normal force is equal to the mass times the gravity, not just the gravity alone.