Forces In Action

Question 1

Equation for resultant force

Answer 1

F = ma
Mass x Acceleration

Question 2

If mass is constant, what is the relationship between force and acceleration?

Answer 2

They are directly proportional

Question 3

If the force is constant, what is the relationship between acceleration and mass?

Answer 3

Acceleration is inversely proportional to the mass
a ∝ 1/m

Question 4

Define a Newton

Answer 4

The resultant force that will give a mass of 1 kg and an acceleration of 1 ms⁻² in the direction of the force

Question 5

Define weight

Answer 5

The gravitational force acting on the object

Question 6

How do you calculate weight?

Answer 6

Mass x Gravitational force

Question 7

What is the centre of gravity?

Answer 7

The point through which the entire weight of an object appears to act

Question 8

What is the centre of mass?

Answer 8

The point through which the mass of the object acts

Question 9

Experiment to find the centre of gravity

Answer 9

1. Suspend the object freely from a point.
2. Use a plumb-line to draw a straight vertical line on the object.
3. Repeat steps using a different suspension point
4. Determine the point of intersection between the straight lines.
5. The point of intersection will show you where the centre of gravity is acting.

Question 10

What does a free body diagram show?

What are the forces that you might see on a free body diagram?

Answer 10

Where all the forces are acting on a particular object

• Thrust
• Weight
• Friction
• Normal contact force
• Drag
• Tension
• Upthrust

Question 11

What is a vacuum?

Answer 11

A volume of empty matter sometimes called ‘free space’
Where there is a very low pressure so fundamentals can be drawn when there is no influence of air resistance or air particles

Question 12

What is drag?

Answer 12

A resistance force experienced by an object moving through a fluid

Question 13

Factors that affect drag

Answer 13

• Speed of an object
• Cross-sectional area of the object
• The viscosity of the fluid it is moving through

Question 14

What is terminal velocity?

Answer 14

The maximum speed of which an object can fall

Net force = 0
Speed is constant
Drag = Weight
Acceleration = 0
There is no upthrust

Question 15

What is the gradient of a velocity time graph?

Answer 15

The acceleration

Question 17

Define density

Answer 17

The amount of matter in a set volume or the mass per unit volume of a substance

Question 18

How can density be visualised?

Answer 18

How many particles are in a certain volume or the space between the particles?

Can be more using particle arrangement illustrations of solid liquids and gases

Question 19

What do the particles in a dense object look like?

Answer 19

Lots of particles per unit volume with minimal gaps

Question 20

Density of air

Answer 20

1.3 kg m⁻³

Question 21

Density of freshwater

Answer 21

1000 kg m⁻³

Question 22

Density of metal

Answer 22

5000 - 10000 kg m⁻³

Question 23

Density of wood

Answer 23

200 - 800 kg m⁻³

Question 24

Density of a vacuum

Answer 24

0 kg m⁻³

Question 25

How do you calculate the density of an alloy?

Answer 25

- Find the mass of metal A and the mass of B - Add them together - Find the volume of metal A and the volume of metal B - Add them together - Calculate the density (combined mass divided by the combined volume)

Question 26

What is the density of an object dependent on?

Answer 26

The density of an object is ONLY dependent on its material and not the objects shape or size

Question 27

How do you measure the density of an irregular shaped object?

Answer 27

1. Measure its mass using a balance. 2. Measure the volume using a water displacement method. (find the change in water levels or use a displacement can.) 3. Difference in water levels = volume of object

Question 28

Define pressure

Answer 28

The perpendicular force applied per unit cross-sectional area Pressure (Pa) = Force (N) / Area (m²)

Question 29

What is fluid pressure?

Answer 29

The pressure exerted when particles of a fluid collide with a surface/container walls

Question 30

What is a fluid?

Answer 30

A substance that flows

Question 31

How does a fluid produce a normal force?

Answer 31

Fluid produces a pressure which produces a normal force to the surface/contain walls as the forces act at right angles

Question 32

What is the atmospheric pressure?

Answer 32

1.01 x 10⁵ Pa or 101 kPa

Question 33

How is pressure caused underwater?

Answer 33

Pressure underwater is caused by both the water and the atmosphere hpg + 1.01 x 10⁵

Question 34

How do you calculate the change in pressure due to water?

Answer 34

hpg Change in depth x Density of liquid x Gravity

Question 35

How does fluid pressure vary?

Answer 35

It varies with depth in an open system - at lower points, more particles, meaning more weight/mass will be acting on the point causing pressure to increase

Question 36

What is an ISOBAR

Answer 36

A horizontal line of pressure in an open system (Pressure will be the same at all points across the same depth)

Question 37

How is bouncy affected?

Answer 37

The buoyancy of an object depends on the forces that act upon it (the upthrust and weight of an object in fluid)

Question 38

What happens if upthrust = weight?

Answer 38

The object will float because there’s no resultant force acting in the vertical plane

Question 39

What happens when upthrust > weight?

Answer 39

hypothetically the object will accelerate out of the liquid (but this wouldn’t happen)

Question 40

What would happen if an objects weight > upthrust?

Answer 40

The object would sink because there is a resultant force acting downwards in the vertical plane

Question 41

How is an upthrust created?

Answer 41

When an object is submerged in water and the pressure at the bottom of the object is greater than at the top the difference in pressure makes the object push up (upthrust - which is a resultant force)

Question 42

What is Archimedes principle?

Answer 42

The upwards force acting on an object in a fluid is equal to the difference between the forces acting on the top and bottom surfaces F2 - F1 = pgh2A - pgh1A = pgA (h2-h1) = pgA(x) = pgV A(x) - Volume

Question 43

What is upthrust equal to?

Answer 43

The weight of a fluid displaced (even if the object floats)

Question 44

How do you determine the upthrust of a floating object?

Answer 44

1. Determine the mass of an object using a balance. 2. Determine the volume (using equations or water displacement method). 3. Calculate the density (mass/volume). 3. Place the object in water and calculate a height of how much of the object was submerged 4. Find the proportion of the block below the surface of the water.