Chapter 4: Forces in Action

Question 1

mass

Answer 1

The amount of matter in an object

Question 2

what does a greater mass lead to?

Answer 2

greater inertia

Question 3

weight

Answer 3

force experience by mass due to a gravitational force

Question 4

centre of mass

Answer 4

single point where the whole weight of an object appears to act

Question 5

How do you find the centre of gravity of an object?

Answer 5

1) hang object freely from a string
2) vertical line downwards from point of suspension - plumb bob
3) Hang object from different point and draw another vertical line
4) Centre of gravity is where the two points meet

Question 6

What are the types of forces?

Answer 6

• normal contact force
• tension
• friction
• upthrust

Question 7

normal contact force

Answer 7

surface exerts equal but opposite force on an object

Question 8

tension

Answer 8

pulling force on an object from either end of a string

Question 9

friction

Answer 9

force acting opposite to motion

Question 10

upthrust

Answer 10

submerged object experiencing upwards force

Question 11

free body diagram

Answer 11

all forces acting on a single object

Question 12

net force

Answer 12

sum of all the forces acting on an object

Question 13

How do you accelerate an object?

Answer 13

Having a non-zero resultant force

Question 14

What are three ways you can find the resultant force of vectors?

Answer 14

• pythagoras
• sine rule
• cosine rule

Question 15

equilibrium

Answer 15

all forces are balanced and cancelled out

Question 16

triangle of forces

Answer 16

forces form a closed loop when joined tip-to-tail

Question 17

What are the sum of forces when an object is in equilibrium?

Answer 17

0

Question 18

moment

Answer 18

turning effect of a force around a pivot

Question 19

What factors affect moment?

Answer 19

-size of force
-distance from pivot

Question 20

principle of moments

Answer 20

if a body is in equilibrium, the sum of the clockwise moments = sum of the anticlockwise moments

Question 21

Do you need to consider the weight of the turning object in calculations?

Answer 21

only if the line of action is not directly over the pivot

Question 22

What makes an object topple over?

Answer 22

line of action falls outside the base area, a resultant moment occurs, causing it to fall

Question 23

What does it mean if an object has a high centre of mass?

Answer 23

smaller base area

Question 24

What makes an object stable?

Answer 24

• low centre of mass
• wide base area

Question 25

What happens in levers?

Answer 25

effort force acts against the load, causing a rigid rotation

Question 26

What happens when an object’s centre of mass is close to a support?

Answer 26

stronger force acts on the support

Question 27

couple

Answer 27

pair of forces of equal size which act parallel to each other but in opposite directions

Question 28

torque

Answer 28

moment of a couple

Question 29

torque equation

Answer 29

M = Fd

Question 30

Equation for moment

Answer 30

M = F x perpendicular distance from a pivot

Question 31

Describe what happens when a resultant force acts on a body with mass?

Answer 31

Body will accelerate in the direction of the resultant force

Question 32

drag

Answer 32

frictional force that opposes motion as an object moves through a fluid

Question 33

terminal velocity

Answer 33

forces acting on a falling object become balanced so the resultant force is 0, acceleration is 0 and object moving at maximum velocity

Question 34

density

Answer 34

mass per unit volume of a substance
a measure of a substance’s “compactness”

Question 35

density equation

Answer 35

density = mass / volume

Question 36

pressure

Answer 36

amount of force applied per unit area

Question 37

pressure equation

Answer 37

pressure = force / area

Question 38

What happens in a fluid regarding pressure?

Answer 38

particles collide with the object, exerting a force over a specific area

Question 39

what happens in a denser fluid?

Answer 39

more particles in a denser volume, more particles collide and a larger force is exerted, causing a higher pressure

Question 40

What happens as the depth increases?

Answer 40

number of particles above a point increase, weight of the particles add pressure

Question 41

pressure in fluid equation

Answer 41

depth x density x gravitational field strength

Question 42

upthrust

Answer 42

upwards force that fluids exert on objects that are completely or partially submerged in a fluid

Question 43

equation for upthrust

Answer 43

(h2 - h1) x density x g x area

Question 44

archimedes’ principle

Answer 44

when a body is completely or partially submerged in a fluid, it experiences an upthrust equal to the weight of the fluid it has displaced

Question 45

what determines if an object floats or sinks?

Answer 45

average density

Question 46

What makes an object float?

Answer 46

lower density than fluid object will only displace as much volume of water that weighs as much as the object

Question 47

What makes an object sink?

Answer 47

object more dense than fluid
weight of water < weight of object
upthrust < weight

Question 48

what suitable measuring instrument would you use to measure the diameter of the ball?

Answer 48

calliper or micrometer