3 Motion

Question 1

explain how to find the centre of mass of an irregular object

Answer 1

• suspend the object at a point
• suspend a plumb bob from a string directly infront of the object
• draw a line
• suspend the object from another point
• draw another line
• the intersection of the lines = the centre of mass

Question 2

recall archimedes’ principle

Answer 2

the upthrust exerted on a body immersed in fluid (whether partially or fully submerged) is equal to the weight of the fluid that the body displaces
if upthrust<weight, the object will sink

Question 3

recall the principle of moments

Answer 3

for a body to be in equilibrium, the sum of the clockwise moments about any point must be equal to the sum of the anticlockwise moments about the same point

Question 4

explain how to investigate force-extension characteristics

Answer 4

• suspend material from clamp stand adjacent to metre ruler
• apply fudicial marker to ruler to indicate original length
• attach masses to bottom of material
• record x for each mass, plot graph of F/x (gradient=k)
• read values at eye-level, set square to ensure ruler=straight

Question 5

explain how to determine the young modulus of a metal wire

Answer 5

• measure diameter using gauge micrometer (on several points, use mean) calc CSA
• apply diff forces to wire using slotted masses & record extension
• calc stress/strain for each mass
• plot on graph, gradient = young modulus

Question 6

recall newton’s first law of motion

Answer 6

an object will remain at rest or at constant velocity unless acted upon by a resultant force

Question 7

recall newton’s second law of motion

Answer 7

the net force acting on an object is directly proportional to the rate of change of momentum (F=ma)

Question 8

recall newton’s third law of motion

Answer 8

when two objects interact, they exert equal and opposite forces on each other (equal magnitude, opposite direction)