Resultant Forces & Free Body Diagrams
This lesson covers:
1What a 'free body diagram' is
2What a 'resultant force' is
3How to calculate a resultant force from a free body diagram
4What it means for an object to be in 'equilibrium'
forces / direction / magnitude / type
Free body diagrams use arrows to show all of the acting on an object.
The length of each arrow indicates the of that force.
The direction of each arrow indicates the of the force.
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The force is the overall force acting on an object, taking into account all the different forces acting on it.
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Forces acting in opposite directions on the same object can 'cancel out'.
During take-off, a plane has a lift force (upwards force) of 690,000 N and a weight (downwards force) of 600,000 N.
What is the resultant force acting on the plane?
1.15 N downwards
90,000 N upwards
90,000 N downwards
1.15 N upwards
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A resultant force acts upon an object.
Which two properties might be affected by that resultant force?
Direction and mass
Density and speed
Direction and temperature
Speed and direction
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What will be the resultant force acting upon this object?
(force arrows are not drawn to scale)
20 N to the right
0 N - no resultant force
10 N to the right
10 N to the left
10 N to the left
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What will be the resultant force acting upon this object?
(force arrows are not drawn to scale)
25 N to the left
0 N - no resultant force
25 N to the right
2 N to the right
30 N to the left
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What will be the resultant force acting upon this object?
(force arrows are not drawn to scale)
15 N to the left
0 N - no resultant force
45 N to the left
60 N to the left
60 N to the right
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If all the forces acting on an object balance out, then we say that the object is in:
Motion
Equilibrium
Freefall
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The train above is travelling at a constant velocity because the forces acting on it are in equilibrium.
Therefore, the missing force must have a magnitude of newtons to the .
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