Force & Vectors

[futuredoc31]

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Helps please,

Is it always true that the direction of motion is always in the same direction with the force? For example, if a man was to jump straight up in the air, he applies a force down towards the ground. Because of Newton's third law, the group pushes him up, propelling him upwards. In this case, it appears that the direction of motion is opposite to the direction of force applied.

 

[Balantidiumcoli]

Helps please,

Is it always true that the direction of motion is always in the same direction with the force? For example, if a man was to jump straight up in the air, he applies a force down towards the ground. Because of Newton's third law, the group pushes him up, propelling him upwards. In this case, it appears that the direction of motion is opposite to the direction of force applied.

If by force you mean net force then yes. One force can be pushing a mass up let's say while another can be pushing the mass down (this is usually represented as a negative number). The net force is equal to the force pushing up + the force pushing down and the value of the net force determines the direction the mass is heading, + for up - for down. If the net force is 0 then the mass is in equilibrium and isn't moving.

 

[PlumbLine]

Wouldn't it be that the net force determines the direction of acceleration? Not necessarily motion.

 

[contraband]

Yes, net force determines the net direction of acceleration - the change in velocity, not the direction of the velocity itself. A ball that has been thrown upwards has a net force down, but is moving up. Its acceleration (change in velocity) points down, meaning that the velocity will change in the downward direction, but not necessarily move (although it eventually will in this case).