Forces & matter

• What are the three types of deformation mentioned in the study material?

  Stretching, bending, and compressing
• What happens to an object when a single force is applied?

  The object will just move in the force’s direction
• What occurs when forces are applied inwards from opposite sides of an object?

  The object will compress
• What is the role of the reaction force when a force is applied to a spring fixed at one end?

  It is a force from the fixed point that contributes to the overall forces acting on the spring
• What does deformation mean?

  Changing shape
• What is elastic deformation?

  The object returns to its original shape when the load has been removed
• Give an example of elastic deformation.

  An elastic band

  
• What is plastic deformation?

  The object does not return to its original shape when the load has been removed
• Give an example of plastic deformation.

  A spring when pulled too far
• What is the formula for Hooke's Law?

  F = kx
• What does the spring constant \( k \) represent?

  The force required to extend a spring per metre
• In Hooke's Law, what does \( F \) represent?

  The force applied to the spring, in Newtons (N)
• In Hooke's Law, what does \( x \) represent?

  The extension of the spring, in metres (m)
• What does it mean if a force/extension graph has a linear section?

  It indicates elastic deformation and follows Hooke’s Law

  
• What is the gradient of the linear section on a force/extension graph?

  The spring constant \( k \)
• What is the elastic limit on a force/extension graph?

  The point at which the material stops obeying Hooke’s Law

  
• What characterizes a non-linear section on a force/extension graph?

  It indicates plastic deformation and does not follow Hooke’s Law

  
• What happens if the non-linear section of the graph is shallow?

  There is a lot of extension for not a lot of force, making it easy to stretch
• What does it mean if a material is described as "brittle" on a force/extension graph?

  The material snaps instead of stretches after the elastic limit
• How is work done calculated from a force/extension graph?

  Work Done = $\frac{1}{2} kx^2$
• What is atmospheric pressure?

  The total weight of the air above a unit area at a certain altitude
• How does atmospheric pressure change with altitude?

  It decreases with increasing height above the Earth’s surface
• Why does atmospheric pressure decrease with higher elevation?

  There are fewer air molecules above the unit area at higher elevations
• What is a fluid?

  A liquid or a gas
• How does the pressure of a gas in a balloon depend on atmospheric pressure?

  The air exerts an inward force on the outer surface of the balloon
• What happens to a balloon in space compared to on Earth?

  In space, the lower atmospheric pressure allows the gas inside to exert a greater outward force, causing the balloon to expand
• What effect does increasing the number of particles in a balloon have?

  It increases the amount of collisions the balloon surface experiences per second, raising the pressure inside
• What does pressure in a fluid cause?

  A force perpendicular to any surface
• How does pressure vary with depth in a fluid?

  The deeper you are in a fluid, the greater the pressure
• Why does pressure increase with depth in a fluid?

  There is a greater amount of fluid above the object, leading to greater weight and force felt
• How does fluid density affect pressure?

  The denser the fluid, the greater the pressure
• What is the condition for an object to float?

  An object floats if its weight is less than the weight of the water it displaces
• How does a boat float in water?

  A 1000 kg boat will sink until it has displaced 1000 kg of water, provided it doesn’t completely submerge
• What is the buoyancy force?

  The upwards force that counteracts the weight of the floating object
• How is the buoyancy force related to the weight of the fluid displaced?

  The buoyancy force is equal to the weight of the fluid displaced by the object
• Why does a ping pong ball float on water?

  Its density is less than the density of the water, leading to a buoyancy force greater than its weight
• How does increasing depth affect pressure in a liquid?

  Increasing depth leads to greater weight of the water above, resulting in greater pressure
• What is the formula for pressure due to a column of liquid?

  Pressure = height of column × density of liquid × g
• What is the atmosphere?

  The thin layer of air surrounding the Earth
• How does the density of the atmosphere change with altitude?

  The atmosphere gets less dense with increasing altitude