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Gcse question on resultant force

Hey,

so can someone give me a good explanation on what resultant force is. Also how is the resultant force 0 on something with constant velocity as one force has to be larger for the object to be moving. Like in the sky if a plane is flying at constant velocity isn't the thrust going forwards stronger than the air resistance?


Thanks
If the velocity is constant then there is no acceleration and so forces are 'balanced'.

In the example you quote the thrust = air resistance.
Original post by Muttley79
If the velocity is constant then there is no acceleration and so forces are 'balanced'.

In the example you quote the thrust = air resistance.


But isn't lets say a car moving forwards at a constant velocity got a higher forward force than the one pushing it backwards? If so how is the rf 0 in that case?
Basically a resultant force is when you have 2+ forces acting at the same time, usually in different directions.
To get the resultant, you use something called a 'vector sum,' where you pretty much add up the forces :smile:

Not sure how much detail is needed for GCSE as I'm in Scotland, but the aeroplane example, because the velocity is constant, the acceleration is 0, and therefore the thrust is equal to the air resistance, as stated by the above poster. Because the two forces are balanced, (equal and opposite) the resultant will be 0 :smile:
The equation F = ma tells us that if acceleration is zero the there is no resultant force.
The OP is asking how it makes sense though.

In your example, if the thrust was greater than the air resistance, then it would be speeding up. Because in terms of force arrows, the thrust one is bigger.

When velocity is constant, the forces are balanced, and no acceleration as has been said above. This means that the velocity that was reached by a greater thrust force initially stays the same.

It doesn't slow down because the forces are balanced, it's maintained.

If the air resistance got larger it would decelerate and try to bring velocity back down to 0.
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lerjj
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Original post by TheTruthTeller
Hey,

so can someone give me a good explanation on what resultant force is. Also how is the resultant force 0 on something with constant velocity as one force has to be larger for the object to be moving. Like in the sky if a plane is flying at constant velocity isn't the thrust going forwards stronger than the air resistance?


Thanks


You need to be thinking in terms of acceleration, not velocity. Any object travelling at constant velocity will have zero resultant force acting on it. Any object at constant acceleration will have a constant resultant force acting on it (including the special case where both are zero).
Original post by TheTruthTeller
Hey,

so can someone give me a good explanation on what resultant force is. Also how is the resultant force 0 on something with constant velocity as one force has to be larger for the object to be moving. Like in the sky if a plane is flying at constant velocity isn't the thrust going forwards stronger than the air resistance?


Thanks


This is basic stuff, make sure you understand. It's a common misconception.

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