Forces in action

Question 1

What is net resultant force

Answer 1

A net resultant force causes an object to accelerate in the direction of the force.

Question 2

What is a newton

Answer 2

A newton is the measurement of force, defined as the force that gives an object of 1kg mass an acceleration of 1ms^-2

Question 3

What is the difference between mass and weight

Answer 3

Mass is an intrinsic scalar property of an object representing the amount of matter it contains, while weight is the force exerted on that mass due to gravity, making it variable depending on the gravitational context.

Question 4

What is a centre of mass

Answer 4

An imaginary point of an object where the weight of the object appears to act. Any external force applied on the centre of mass will cause a straight line of motion.

Question 5

How do you use a plumb line to find the centre of gravity of a card

Answer 5

Make small holes along the edges of the object made from card. Insert a pin through one of the holes and hold the pin firmly in a clamp. Allow the object to swing freely. It will come to rest with its centre of gravity vertically below the pin. Hang a plumb-line from the pin and draw a line along the vertical string of the plumb-line. Repeat this process for other holes. The centre of gravity will be the point of intersection of the lines.

Question 6

What is friction

Answer 6

The force that arises when 2 surface rub against each other

Question 7

What is drag

Answer 7

The resistive force on an object travelling through a fluid. Changes based on the speed, cross sectional area of object and the density of fluid. Directly proportional to velocity squared.

Question 8

What is tension

Answer 8

The force within a stretched rope

Question 9

What is upthrust

Answer 9

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

Question 10

What is normal contact force

Answer 10

The force that arises when an object rests against another object.

Question 11

What is terminal velocity

Answer 11

The maximum constant speed a free falling object reaches when its net resultant force is 0. When drag is equal to weight, acceleration is 0 and terminal velocity is reached.

Question 12

What is a moment

Answer 12

The turning effect of a force about some axis or point.

Question 13

How to calculate moments

Answer 13

Force * Perpendicular distance from line of force to pivot or axis.

Question 14

What is a couple

Answer 14

An equal and opposite pair of forces applied to a body in parallel along different lines, causing the body to rotate without translational movement.

Question 15

What is torque

Answer 15

The moment of a couple, calculated by one of the forces * perpendicular distance between forces.

Question 16

What is the principle of moments

Answer 16

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

Question 17

What is density

Answer 17

Mass per unit volume of a substance

Question 18

How to find density of an object

Answer 18

Using a digital balance to find the mass. Use a measuring cylinder to find the volume of a liquid. Calculate the volume of a regular shaped object by measuring its sides, using a ruler, a digital calliper or micrometer. Calculate the volume of an irregular object by placing it into a body of water in a measuring cylinder then measuring the change in water levels.

Question 19

What is pressure

Answer 19

Force per unit cross sectional area.

Question 20

How does pressure in water work

Answer 20

An object immersed in a column of fluid experiences pressure due to the weight of the fluid above it. The pressure at the base of a column of fluid is given by the equation p=hpg. At the base, the force is the weight of the fluid, so mg/A equals pressure. Mass is equal to density * volume, therefore pgV/a equals pressure. Volume divided by area equals height, therefore hpg = P

Question 21

What is Archimedes principle

Answer 21

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. The pressure at the bottom surface of the object is greater than at its top surface. An object will sink if the upthrust acting up is smaller than the weight acting down. For a floating object, the weight is equal to the upthrust, so the object’s weight is equal to the weight of the fluid it displaces.