Topic 15 - Forces and Matter Flashcards
SP15a - What are the three things a force can do to an object?
- Change shape(/size)
- Change direction
- Accelerate (Decelerate)
SP15a - What is the name for a force changing the shape of an object and what is required for it to occur?
It is called deformation and requires two forces rather than just one.
SP15a - What does it mean if an object elastically deforms?
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.)
SP15a - What does it mean if an object inelastically deforms?
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.)
SP15a - How may some objects behave elastically and inelastically?
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]
SP15a - What is the extension of a spring?
The change in length of a spring when a force is applied
New length - old length = extension
SP15a - How would you describe the relationship between force and length of a spring
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).
SP15a - What is the relationship between extension and force of a spring and rubber band?
- 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
SP15b - What is a spring constant?
The force (N) required to produce and extension of 1 metre
SP15b - What is the equation linking force and spring constant?
F = k × x
Force (N) = Spring constant (N/m) × Extension (m)
SP15b - What is the relationship between force and extension?
F ∝ x (Directly proportional)
SP15b - What does the gradient of a Force/extension graph show you?
Sign gradient is Δy÷Δx it would be force/extension which will give you the spring constant of a spring
SP15b - How may you be able to tell that a spring has a higher spring constant by holding it?
Stiffer springs have a higher spring constant (As they require more force to extend)
SP15b - How do you calculate the work done when stretching a spring?
E = 1/2 × k × x²
Energy transferred by stretching (J) = 1/2 × Spring constant × Extension²
SP15b CP - Describe how to find the spring constants of different springs.
- Set up your equipment as shown
- 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
SP15c - What is the formula for pressure?
P = F ÷ A
Pressure (Pa) =
Force [normal to surface] (N) ÷ Area of that surface (m²)
SP15c - What are the units for pressure?
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)
SP15c - What are fluids?
Liquids or gases
(Because they f̶l̶o̶o̶o̶d̶ flow)
SP15c - What is atmospheric pressure?
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)
SP15c - What two things affect the pressure exerted by a fluid?
- 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
SP15c - When calculating total pressure when underwater, what must you do?
Find the pressure exerted by the water and add 100,000 Pa of air pressure
SP15c - Why does a bag of crisps sealed at sea level expand when at higher altitudes?
- 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
SP15d - What formula calculates the pressure due to a column of liquid?
P = h × ρ × g
Pressure [due to column] (Pa) =
height of column (m) × density of fluid (kg/m) × gravitational field strength (N/kg)
SP15d - What is upthrust?
The upward force exerted on the bottom of an object in a liquid.
SP15d - How do you calculate upthrust?
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
SP15d - If an object is floating what does this mean?
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)
