Chapter 4: Turning effects of forces

Question 1

pivot

Answer 1

a fixed point about which a lever turns; also known as the fulcrum

Question 2

turning effect

Answer 2

when a force causes an object to rotate or would make the object rotate if there were no resistive forces.

Question 3

moment

Answer 3

The turning effect of a force about a pivot given by force x perpendicular distance from the pivot

Question 4

equilibrium

Answer 4

when no net force and no net moment act on a body.

Question 5

when a beam is balanced…

Answer 5

-the forces must be balanced (no resultant force), upward forces = downward forces.
-the turning effects of the forces on it must be balanced (no resultant turning effect)

Question 6

moment of the force formula

Answer 6

force x perpendicular distance from the pivot

Question 7

anticlockwise

Answer 7

turning in the opposite direction from the hands on a clock

Question 8

clockwise

Answer 8

turning in the same direction as the hands on a clock

Question 9

principle of moments

Answer 9

when an object is in equilibrium the sun of anticlockwise moments about any point equals the sum of clockwise moments about the same point.

Question 10

stable

Answer 10

an object that is unlikely to topple over, often because it has a low centre of gravity and a wide base.

Question 11

unstable

Answer 11

an object that is likely to topple over, often because it has a high centre of gravity and a narrow base.

Question 12

Center of gravity

Answer 12

All the mass of the object could be located here and the object would behave the same (when ignoring any spin).

Question 13

Lamina

Answer 13

flat, two-dimensional shape

Question 14

Equilibrium Description(3)

Answer 14

-the glass is upright. Its weight acts downwards and the contact force of the table acts upwards. The two forces are in line, and the glass is in equilibrium.
-The glass is tilted slightly to the right, and the forces are no longer in line. There is a pivot at the point where the base of the glass is in contact with the table. The line of the glass weight is to the left of this pivot, so it has an anticlockwise moment, which tends to tip the glass back to its upright position.
-The glass is tipped further. Its weight acts to the right of the pivot and has a clockwise moment, which makes the glass tip right over.

Question 15

The moment of a force is bigger (3)

Answer 15

-The moment of a force is bigger if the force is bigger.
-The moment of a force is bigger if it acts further from the pivot
-The moment of a force is greatest if acts 90 degrees to the object it acts on.

Question 16

Find the centre of mass of an irregular object (6)

Answer 16

-Use a sharp object or a hole puncture to cut holes in 3 different corners (near the edge) on the lamina. they must far apart.
-Fix hole A on the lamina horizontally making sure it can swing properly.
-Hang the plumbline directly in the front of the lamina, wait for the plum bob to come to a rest and then proceed to mark a cross or dot behind the string.
-Take the string and the lamina off the clamp stand gently and from hole A draw a dotted line along the marked indicator.
-Repeat steps 2, 3, and 4 for holes B and C.
-Conclusion- Where the 3 lines intersect, is the center of mass/ gravity on the lamina.

Question 17

Principle of Moments experiment

Answer 17

-Put a nail into the first cork and clamp it to the stand followed by the meter ruler that must be suspended horizontally at 50 cm.
-Plant the second cork to ensure the meter ruler is in equilibrium.
-Place the m1 weights d2 centimetres away from the pivot on either side of the pivot (the corresponding weight can be moved until the meter ruler is balanced to or away from the pivot.
-Note the results in the table.
-Repeat the experiment with different weights.

Question 18

Principle of Moments experiment (precautions)

Answer 18

-Make sure the nail is fitted properly into both the corks to balance the ruler better and tightly.
-The meter ruler is at its centre and balanced.

Question 19

Principle of Moments experiment (safety precautions)

Answer 19

-Wear safety glasses and a lab coat.
-Clamp the retort stand to the bench with a g clamp to avoid it falling on someone’s feet.
-Place an obstacle such as a stool to keep feet beneath the meter ruler/ mass from crushing someone’s feet.