Forces in action

Question 1

newton

Answer 1

A force of 1 newton will give a mass of 1 kg an acceleration of 1 ms^-2 in the direction of the force

Question 2

Weight

Answer 2

The gravitational force acting on an object through its centre of mass

Question 3

Friction

Answer 3

The force that arises when two objects rub against each other

Question 4

Drag

Answer 4

The resistive force on an object travelling through a fluid (e.g. air or water); the same as friction

Question 5

Tension

Answer 5

The force within a stretched cable or rope

Question 6

Upthrust

Answer 6

An upward buoyancy force acting on an object when it is in a fluid

Question 7

Normal contact force

Answer 7

A force arising when one object rests against another object

Question 8

Factors affecting drag

Answer 8

• speed of the object (drag ∝ speed^2)
• cross-sectional area of the object

Question 9

Free fall

Answer 9

At the instant an object starts to fall, the only force (resultant force) acting on an object is its weight, which makes it accelerate downwards with an acceleration of g, 9.8 ms^-2.

As the object falls, its speed increases, and this in turn increases the drag acting to oppose the object’s motion. The resultant force downwards decreases, so its instantaneous acceleration also decreases.

Eventually, the object reaches terminal velocity when the drag is equal and opposite to its weight. The resultant force (and therefore acceleration) is zero, so the object travels with constant speed.

Question 10

Investigating terminal velocity in fluids

Answer 10

IV - mass of ball
DV - time taken for ball to travel certain intervals
CV - fluid

Heavier ball has a greater weight, meaning it takes longer for drag to equal its weight, so it is able to reach a greater terminal velocity.

Question 11

Moment

Answer 11

Turning effect of a force about some axis or point
OR Moment = Force x perpendicular distance of the line of action of the force from the axis or point of rotation

Question 12

Principle of moments

Answer 12

For a body in rotational equilibrium, the sum of the anticlockwise moments about any point is equal to the sum of clockwise moments about that same point

Question 13

Couple

Answer 13

A pair of equal and opposite forces acting on a body, but not in the same straight line

Question 14

Torque

Answer 14

The moment of a couple

Question 15

Centre of mass/gravity

Answer 15

The point through which the weight of an object seems to act

Question 16

Investigating centre of mass

Answer 16

IV - orientation of lamina
DV - straight line from plumb
CV - lamina

Question 17

Density

Answer 17

Mass per unit volume

Question 18

Pressure

Answer 18

Normal force exerted per unit cross-sectional area

Question 19

Archimedes’ principle

Answer 19

The upthrust exerted on a body immersed in fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces