4 - Forces in Action

Question 1

Energy transfers examples

Answer 1

heating (thermal), electrical, light, sound, kinetic forces (mechanical work), nuclear (radiation)

Question 2

Energy stores examples

Answer 2

gravitational potential, chemical potential, thermal store, elastic potential, nuclear potential, magnetic potential, kinetic store

Question 3

Contact forces

Answer 3

air resistance, friction, upthrust, tension, compression, thrust

Question 4

Non-contact forces

Answer 4

weight, electrostatic, magnetic

Question 5

4 Fundamental forces

Answer 5

gravitational (acts on anything with mass e.g. protons, neutrons, electrons), electrostatic/electromagnetic, (acts on anything with charge e.g. protons, electrons), weak nuclear, strong nuclear

Question 6

If resultant force acting on an object is 0…

Answer 6

object is stationary or remains at constant speed as forces are balanced

Question 7

Centre of mass

Answer 7

The point at which an object’s mass is centred or concentrated, the point through which a single force on the body has no turning effect. For regular symmetrical objects, the COM is the centre of the object

Question 8

Centre of gravity

Answer 8

Weight is caused by the attraction of every atom inside an object to every atom inside the Earth. The sum of all of these forces appear to act from a single point for any object, this is the centre of gravity

Question 9

How to find COM for irregular objects

Answer 9

First, make a hole in the material and hang. Hang a piece of string from it with a weight on the end so you can trace the line (plumb line). Make another hole in a different place and do the same thing. Where the lines cross is the centre of mass for that object

Question 10

What factors affect stability

Answer 10

width of base and height of centre of mass. More stable objects have wide bases and low COMs

Question 11

What is a moment?

Answer 11

the turning effect of a force and will act around a pivot. A moment can act clockwise or anticlockwise

Question 12

Moment equation

Answer 12

Moment = Fd
Moment (Nm) = Force (N) x perpendicular distance to the line of action of the force (m)

Question 13

If a body is in equilbrium…

Answer 13

turning force resultant force is 0, the sum of the clockwise moments is equal to the sum of the anti-clockwise moments (CW=ACW

Question 14

Stable equilibrium:

Answer 14

If a body is displaced from the equilibrium position then released, it will return to the equilibrium position

Question 15

Unstable equilibrium:

Answer 15

If a body is displaced from the equilibrium position then released, it will not return to the equilibrium position.

Question 16

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 a couple?

Answer 17

two equal and opposite forces acting on a body but on different lines of action

Question 18

Density is

Answer 18

the amount of mass per unit volume measured in kgm^-3. It is an intrinsic property

Question 19

Density equation

Answer 19

Density = mass (kg) /volume (m^3)

Question 20

When will an object float in water?

Answer 20

if its density is lower than water (1000kgm^-3)

Question 21

Upthrust

Answer 21

the weight of the fluid displaced or the difference in pressure between the top and bottom of an object

Question 22

Effect of volume on upthrust

Answer 22

Bigger the volume, bigger the upthrust as they are directly proportional (object material doesnt matter but material submerged in does)

Question 23

Archimedes’ Principle

Answer 23

the volume of the fluid displaced is equal to the volume of the part of the body submerged