[Part 3] P8- Forces in balance 🚂🏎️

Question 1

What is mass ?

Answer 1

• mass, is the quantity of matter in an object
• ; it can also be known as, a measure of the difficulty of changing the motion of an object

Question 2

What is the unit of mass ?

Answer 2

• the unit of mass is the kilogram [kg]- this is the standard unit for mass, and therefore it is never converted

Question 3

What quantity is mass ?

Answer 3

• mass is a scalar quantity because, it has no direction.

Question 4

What else can you tell me about mass ?

Answer 4

• the mass of an object, doesn’t depend on where the object is.

Question 5

What is weight ?

Answer 5

• weight, is the force acting on an object due to gravity.
• and the unit of weight, is the newton (N)

Question 6

What’s a fact you can tell me about weight ?

Answer 6

• unlike mass, weight does depend on where it is.
• and the weight of an object, is directly proportional to the mass of an object. [therefore, if the weight is doubled, so is the mass]

Question 7

How can we determine an object’s weight?

Answer 7

• we can determine an object’s weight, by using a newton meter.
• ; it’s also called a calibrated spring-balance.

Question 8

RECAP: What’s gravitational field strength?

Hint: measure of

Answer 8

• gravitational field strength, is a measure of the force of gravity, in a particular location.
• ; the gravitational field strength, depends on where you are.

Question 9

Give an example of gravitational field strength

Hint: 📦

Answer 9

• the gravitational field strength, depends on where you are.
• For example on Earth, an object with a mass of 100kg, will have a weight of 980N because the gravitational field strength on the Earth’s surface is 9.8N/kg
• ; on the moon, the same object will still have a mass of 100kg, but a weight of 160N- since the gravitational field strength of the moon, is 1.6kg.

Question 10

Define the term ‘centre of mass’ [2]

Answer 10

• the centre of mass, is where the weight of an object [the force due to gravity] can be considered to act at a single point.
• in other terms, the centre of mass of an object is: the point at which it’s mass, can be thought of as concentrated.

Question 11

How can you find the centre of mass, of a regular shape ?

Hint: lines of symmetry

Answer 11

• draw in the lines of symmetry for these regular shapes, and the centre of mass of a regular shape, is where the lines of symmetry cross.

Question 12

Describe an experiment to find the centre of mass, of an irregularly shaped piece of card. 🃏

Hint: suspend, plumbline

Answer 12

• the irregular shape in this expirement, is a cardboard cut out
• If the card is hung from a thread, the centre of mass is always below, in line with the thread.
• suspend the card, and attach a
  plumb line. Using a pencil, draw
  a line along the plumb line.
• and repeat the last step from a different point. The centre of mass is where the lines cross. [You need at least 3 lines.]

Question 13

Describe steps one to two, about how to draw a vector diagram ? [the parallelogram of forces] ▰

Hint: scale drawing

Answer 13

1) first make a scale drawing, to show the forces involved [e.g, 1cm= 1N]

2) draw a point to show a free-body diagram, and then use a ruler to draw a x cm arrow, to represent the x newton force.

3) measure an angle of x* degrees using a ruler, and then use a ruler, to draw an x cm arrow to represent the x N force.

4) then create a parallelogram. To do this, copy the x cm line and position it, at the head of the x cm force vector.

5) copy the x cm line, positioning it at the head of the x force vector

6) draw a line from the tails of the force vectors, to the other side of the parallelogram

7) and finally measure the length of the vector, and work out the resultant force it represents

Question 14

Describe how to resolve a force [into two separate components] ? ↗️

Answer 14

1) first draw a scale vector diagram of the force [e.g- 1cm= 10N]

2) and draw faint lines, to show the horizontal and vertical axes.

3) then use a protractor, to measure the angle from the horizontal.

4) now use a ruler, to draw the vector [showing the x N force]

5) and then draw dotted lines from the head of the vector, to the horizontal and vertical axes.

6) now draw the horizontal and vertical components and finally use a ruler, to determine their magnitude.

Question 15

What’s stability ?

Answer 15

• stability, is the tendency of an object, to stay in a particular position.

Question 16

With reference to the centre of mass, when does toppling occur ?

Hint: line through

Answer 16

• toppling occurs, when a line through the centre of mass, is outside the pivot

Question 17

How can stability be increased ?

Answer 17

• stability can be increased by:
• lowering the centre of mass
• by giving the object a wider base

Question 18

Explain how lowering the centre of mass, can increase stability

Answer 18

• stability can be increased by:
• lowering the centre of mass.
• This is because, the base could be made out of a heavier object, or the base could have been made bigger- this would also lower the centre of mass.

Question 19

What’s equilibrium [in physics] ?

Answer 19

• equilibrium, means that all forces that are acting on an object, are balanced.

Question 20

What’s the difference between stable equilibrium 🆚 unstable equilibrium ? 🧺

Answer 20

• if a body’s in stable equilibrium, it means it comes back to its original position, when displaced- [e.g- a hanging basket]
• ; if a body’s in unstable equilibrium, this means it doesn’t come back to its original position, when displaced. [e.g- a pencil balanced on its end]

Question 21

What’s the difference between stability 🆚 equilibrium ?

Answer 21

• stability, is the the tendency of an object, to stay in a particular position.
• ; equilibrium, means that all forces that are acting on an object, are balanced.

Question 22

What does the term ‘resolving a force’ mean ?

Answer 22

• resolving a force, simply means to split one force arrow, into two perpendicular components.

Question 23

When resolving a force, what’s a component ?

Answer 23

• when resolving a force, a component is:
• two forces that have an overall effect.
• [the ‘horizontal’ and ‘vertical’ components, are part of a forceJ