SP15 - Forces and Matter ✓ Flashcards

1
Q

SP15a - What are the three things a force can do to an object?

A
  • Change shape(/size)
  • Change direction
  • Accelerate (Decelerate)
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2
Q

SP15a - What is the name for a force changing the shape of an object and what is required for it to occur?

A

It is called deformation and requires two forces rather than just one.

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3
Q

SP15a - What does it mean if an object elastically deforms?

A

The forces change the object’s shape but it returns back to its original shape when forces are removed. (e.g spring, diving board, and archer’s bow.)

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4
Q

SP15a - What does it mean if an object inelastically deforms?

A

The forces change the object’s shape and it doesn’t return back to its original shape when forces are removed. (e.g Clay, Blu-tac, and spoons.)

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5
Q

SP15a - How may some objects behave elastically and inelastically?

A

Some objects (like springs for example) will behave elastically. However, when the forces exceed a certain amount, they will become permanently deformed, behaving inelastically and keeping its new shape.

[Life Lesson #44: Don’t overextend yourself]

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6
Q

SP15a - What is the extension of a spring?

A

The change in length of a spring when a force is applied

New length - old length = extension

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7
Q

SP15a - How would you describe the relationship between force and length of a spring

A

It is a linear relationship (straight line) as long as the spring behaves elastically.

Once it is permanently deformed, the relationship is non-linear (curved).

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8
Q

SP15a - What is the relationship between extension and force of a spring and rubber band?

A
  • Spring: They are directly proportional as it would be a straight line through the origin.
  • Elastic band: It behaves completely inelastically with a non-linear relationship
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9
Q

SP15b - What is a spring constant?

A

The force (N) required to produce and extension of 1 metre

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10
Q

SP15b - What is the equation linking force and spring constant?

A

F = k × x

Force (N) = Spring constant (N/m) × Extension (m)

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11
Q

SP15b - What is the relationship between force and extension?

A

F ∝ x (Directly proportional)

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12
Q

SP15b - What does the gradient of a Force/extension graph show you?

A

Sign gradient is Δy÷Δx it would be force/extension which will give you the spring constant of a spring

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13
Q

SP15b - How may you be able to tell that a spring has a higher spring constant by holding it?

A

Stiffer springs have a higher spring constant (As they require more force to extend)

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14
Q

SP15b - How do you calculate the work done when stretching a spring?

A

E = 1/2 × k × x²

Energy transferred by stretching (J) = 1/2 × Spring constant × Extension²

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15
Q

SP15b CP - Describe how to find the spring constants of different springs.

A
  • Set up your equipment as shown ( Clamp a spring, attach weights, clamp ruler, measure extension)
  • Measure the length of the spring without any weights at eye-level
  • Add 1 newton (100g) weights one at a time, measuring the new length at eye level each time
  • Take away the original length from all your values to get the extension
  • Repeat a few times and take the average of your results for reliability
  • Plot a graph of force/extension and calculate the gradient of the line. This will be the spring constant
  • If you want to find the work done for a particular extension, square that extension, divide by 2 and then multiply by the spring constant
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16
Q

SP15c - What is the formula for pressure?

A

P = F ÷ A

Pressure (Pa) =

Force [normal to surface] (N) ÷ Area of that surface (m²)

17
Q

SP15c - What are the units for pressure?

A

Pa - Pascals, which is equivalent to N/m²

(however the m in N/m² can be changed to any other metric length value but won’t be equal to 1 Pa)

18
Q

SP15c - What are fluids?

A

Liquids or gases

(Because they f̶l̶o̶o̶o̶d̶ flow)

19
Q

SP15c - What is atmospheric pressure?

A

The pressure exerted perpendicular to any surface by the air at all times. It is highest at sea level around 100,000 Pa (1 atm)

20
Q

SP15c - What two things affect the pressure exerted by a fluid?

A
  • Depth of the fluid: The more particles above you, the higher pressure you will experience as more particles can produce a higher force. This is why pressure is highest at sea level and reduces as you increase altitude
  • Density of fluid: The denser the fluid you are in, the more particles there are in a fixed volume, the more particles can produce a force. This is why water pressure is higher than air pressure
21
Q

SP15c - When calculating total pressure when underwater, what must you do?

A

Find the pressure exerted by the water and add 100,000 Pa of air pressure

22
Q

SP15c - Why does a bag of crisps sealed at sea level expand when at higher altitudes?

A
  • When sealed at sea level, the air inside the bag will around 100,000 Pa
  • When taken to a higher altitude, the pressure outside the bag decreases
  • As the pressure inside the bag (acting outwards) is greater than outside the bag (acting inwards), the bag expands
23
Q

SP15d - What formula calculates the pressure due to a column of liquid?

A

P = h × ρ × g

Pressure [due to column] (Pa) =

height of column (m) × density of fluid (kg/m) × gravitational field strength (N/kg)

24
Q

SP15d - What is upthrust?

A

The upward force exerted on the bottom of an object in a liquid.

25
Q

SP15d - How do you calculate upthrust?

A

Difference in pressure between top and bottom of the object multiplied by the surface area of the bottom of the object

[Upthrust = Δh × ρ × g × surface area (m²)]

OR

Upthrust is the weight (in Newtons) of the liquid displaced when an object is placed in the liquid

26
Q

SP15d - If an object is floating what does this mean?

A

The density of the object is less than the liquid it is in. The lower the density, the better it floats (more will be above the liquid surface)