Question about 3rd law and normal force

[kmikias]

Hi,guys ...i have a question in my mind always confused me just like Newton 3rd law but this one is different.

here is my question.
I always confuse with the normal force and weight force which is mass * gravity.

for example let's say a coin tossed straight upward,and reaches its highest point and falls back down again.

1.here is my question when the coin is moving upward after it released. is it the force down or up?....because i am confuse with the normal force and the weight force that's pulls the coin down.I know the normal force always be up and weight force be down.but how do we know the force is up and down. and also how do we know if it is decreasing and increasing.

2. my second question how about if the coin at highest point . is the force will be down or up ..but my guess is 0 because the acceleration will be zero.



thanks.

 

[edziura]

"here is my question when the coin is moving upward after it released. is it the force down or up?....because i am confuse with the normal force and the weight force that's pulls the coin down.I know the normal force always be up and weight force be down."

First, the 'normal force' is only present on an object when the object is supported (as in resting on the floor) and is the force which prevents the force of gravity from accelerating the object down. It is also referred to as the 'support force'.

So the coin tossed in the air has no normal force acting on it, only the force of gravity, which always acts downward.

"my second question how about if the coin at highest point . is the force will be down or up ..but my guess is 0 because the acceleration will be zero."

Love this question. Think of it this way: acceleration the rate of change of velocity. If the rate of change of velocity (acceleration) is zero, then when the coin reaches the highest point (where its velocity is instantaneously zero), its velocity stops changing, which means it would simply stay there and not start moving downward. The acceleration cannot be 0 at the highest point, even if the velocity is.

 

[baba89]

Hi there,

Your question about the normal force and weight force is a common one, and it's important to understand the difference between the two. The third law of motion states that for every action, there is an equal and opposite reaction. In the case of the coin being tossed upward, the action is the force exerted by your hand on the coin, and the reaction is the force exerted by the coin on your hand. This is why you feel a slight pushback when you toss the coin.

Now, let's break down the forces acting on the coin as it moves upward and reaches its highest point. The force of gravity is acting downward on the coin, and this is known as the weight force. The normal force, on the other hand, is the force exerted by the surface the coin is on (in this case, your hand) to support the weight of the coin. So, when the coin is moving upward, the force of gravity is still acting downward, but the normal force is acting upward to balance it out.

At the highest point, the coin has stopped moving and is momentarily at rest. This is because the force of gravity and the normal force are equal and opposite, resulting in a net force of 0. This is also why the acceleration is 0 at this point.

I hope this helps clarify the concept of normal force and weight force for you. It's important to remember that they are two different forces, with the normal force always acting perpendicular to the surface the object is on. Let me know if you have any further questions. Keep exploring and learning!