Forces , density and pressure

• What are the two main types of forces?

  Contact forces and Non-Contact forces
• What are the types of contact forces?


  • Active forces: push or pull
  • Resistive forces: air resistance, friction
  • Tension: stretching something
  • Compression: squishing something
  • Reaction: opposing force
  • Twisting force: twist or turn
  • Upthrust: pushes upward from a liquid
• What are the types of non-contact forces?

  • Gravitational: attractive force between objects with mass
  • Magnetic: attractive force between magnetic materials
  • Electrical: attractive/repulsive force between charged materials
• What is the difference between scalar and vector quantities?

  Scalar has only magnitude, while vector has both magnitude and direction
• What are examples of vector quantities?

  • Force
  • Displacement
  • Velocity
  • Acceleration
  • Momentum
• How do we represent forces as vectors?

  Forces are represented by arrows starting on the object
• What does friction do to moving objects?

  Friction always tries to slow moving objects down
• What is air resistance also known as?

  Drag
• What are the steps to find the resultant force of two forces at right angles?

  1. Draw a point to represent the object
  2. Create an appropriate scale
  3. Draw the first force arrow
  4. Measure the angle for the second force
  5. Draw the second force arrow at the measured angle
  6. Create a parallelogram using faint lines
  7. Draw a diagonal from the original point to the opposite corner
  8. Measure the diagonal and angle to find the resultant force
• What is work done when a force moves through a distance?

  Work done = Force × Distance moved in direction of force
• What is Hooke's Law?

  Hooke's Law states that the force needed to extend or compress a spring is proportional to the distance it is stretched or compressed
• What is the formula for weight?

  Weight = Mass × Gravitational Field Strength

  • Weight is measured in Newtons (N)
  • Mass is measured in kilograms (kg)
  • Gravitational field strength is measured in Newtons per kilogram (N/kg)
• What are the characteristics of elastic and plastic materials?

  • Elastic: Returns to original shape after force is released
  • Plastic: Keeps new shape after force is released
• What is the formula for pressure?

  Pressure = Force / Area
• How does pressure in liquids change with depth?

  • Pressure in liquids acts in all directions
  • Greater depth results in greater pressure due to more liquid mass above
• What happens to an object in a liquid if its weight is greater than the upthrust?

  The object will sink
• What is standard atmospheric pressure measured in?

  760 mmHg
• What does Boyle's Law state about the relationship between pressure and volume of a gas?

  • At a fixed temperature and mass of gas, volume is inversely proportional to pressure
  • Formula: \( PV = \text{constant} \)
• What happens to the volume of a gas when the pressure increases at constant temperature?

  The volume decreases
• What occurs to a balloon when a vacuum is applied?

  The balloon expands as air particles try to fill the vacuum
• What happens to a can when heated and then placed in cold water?

  The can collapses due to lower air pressure inside
• What is the significance of the Magdeburg hemispheres demonstration?

  • Shows the effect of atmospheric pressure
  • When a vacuum is created, the pressure outside is greater, making it hard to pull apart
• What is the unit of pressure?

  Pascals (Pa)
• How does pressure in gases change with volume according to Boyle's Law?

  As volume decreases, pressure increases