6.2 - balanced forces

what is equilibrium?

• at rest

• moving at constant velocity

• balanced forces are acting on it, meaning the resultant force is zero

is an object in equilibrium when its moving at constant velocity?

yes!

when is an object in equilibrium?

when two balanced (equal and opposite) forces are acting on a point object, therefore their resultant force is zero

what does balanced mean in regards to forces?

the two forces acting on a point object are equal and opposite to each other

what is a point object?

an object whose dimensions are ignored to simplify calculations

what does it mean for two forces acting on a point object to be equal and opposite to each other?

they are balanced forces, therefore their resultant is zero and the object is at equilibrium

what is the resultant force when an object is at equilibrium?

zero

why is the resultant force zero when an object is at equilibrium?

because the forces acting on the object are balanced

what is the support force?

• upwards force on the object due to the surface to keep the object at vertical equilibrium

• equal to the object’s weight

why is there a support force?

to keep the object at vertical equilibrium, so it doesn’t fall through the surface

support force = ?

support force = object weight

object weight = ?

object weight = support force

why does the support force = object weight?

• object weight is the downwards force acting on the surface

• when the object is at equilibrium, forces must be balanced (equal and opposite)

• the surface exerts an equal force on the object, i.e., support force, to keep the object in equilibrium

• therefore support force = object weight

when does S = W?

when the object is at equilibrium

what is weight?

the force of gravity acting on an object

when three forces act on a point object, when is the object at equilibrium?

• when any of the two forces is equal and opposite (balanced) to the third force

• therefore the resultant is zero

when three forces act on a point object, how do you check if the object is at equilibrium?

• resolve each force along the same parallel and perpendicular lines

• balance the components along each line

here

worked example 1 questions

worked example 2 questions

worked example 3 questions

what is a force diagram?

diagram depicting the forces in play, including force magnitude and direction

here

what does rough mean?

friction is involved, and must be included in the resultant force

how do you test for three forces in equilibrium?

here

questions about testing for 3 forces in equilibrium