Forces in Equilibrium

Question 1

what does newtons first law of motion state

Answer 1

• that an object will remain at rest or continue to move with a constant velocity
• unless acted upon by a resultant external force

Question 2

if you had a rock in space that was stationary or moving at a constant velocity, how would its motion change if two or more forces were acting on it and why

Answer 2

• the rock might still remain stationary or at its same velocity
• because it could still be that no resultant force is acting on the rock

Question 3

when is a body in equilibrium

Answer 3

• when it is acted on by a number of forces

- but the resultant or sum of them is zero

Question 4

what is the centre of gravity of an object

Answer 4

the point at which the weight of the object is said to act

Question 5

what do you do if you want to isolate the forces acting an a single object

Answer 5

draw a free-body force diagram

Question 6

you have a rock climber pushing his feet against the vertical face of a cliff with his partner pulling him upwards with a rope. what would the free-body force diagram of the man look like

Answer 6

• his weight would always be acting directly downwards
• his reaction force would be pointing from his feet through his body and to his face (away from the cliff face)
• there would be tension force upward through the rope pulling him upwards

Question 7

if the man is not moving upwards or downward but all these forces are still acting on him, what relationship do these forces have

Answer 7

• the sum of the horizontal and vertical planes must equal 0
• meaning the product of the magnitude and direction of his weight must equal the sum of the magnitude of the reaction and tension force, with their direction taken into account (aka the angle theyre acting at)

Question 8

a vertical line is drawn in between the reaction force acting slightly to the left from the vertical and the tension force acting slightly to the right. using the angles they both make from this line, how can you write out an equation to show how the sum of the vertical planes equal 0 if reaction force is P, tension force is T and weight is W

Answer 8

(P cos theta + T cos theta) - W = 0

Question 9

what equation would be written to show how the horizontal planes equal 0

Answer 9

T sin theta - P sin theta = 0