P5 - Forces 🤢

• What is a contact force

  When objects have to physically be touching to feel a force
• Give four examples of non-contact forces

  Normal force, friction, air resistance, tension
• What is a non-contact force

  Objects don’t have to be physically touching to feel a force
• Give three examples of a non-contact force

  magnetism, electrostatic force, gravity
• What is a scalar force?

  A force that only has magnitude
• What is a vector force?

  A force that has both magnitude and direction
• Give five examples of a scalar

  distance, speed, mass, energy, temperature
• Give five vector quantities

  Displacement, velocity, acceleration, force, momentum
• How do you calculate a resultant force using a scale diagram?

  1. Draw on the forces to scale and in the correct direction
  2. Connect the two lines and measure the length or use pythagoras’ theorem
  3. Use SOHCAHTOA to find the angle of the force
• What does it mean if there is no resultant force?

  The object is not accelerating or decelerating
• What is the formula for weight?

  Weight = mass x gfs
• Hooke’s Law: The extension of an object is directly proportional to the force applied to it
• Elastic deformation: an object returns back to its original size and shape after being stretched or compressed
• Inelastic deformation: An object does not return to its original size or shape after being stretched or compressed
• Hooke’s Law practical:

  1. Set up the equipment as seen in the diagram
  2. Add a mass to the spring to change the force applied
  3. Measure the extension with a ruler - avoid systematic error by lining up the 0cm with the bottom of the spring, avoid parallax error by reading the ruler at eye level
  4. Change the mass on the spring and continue to measure the extension for every weight
  5. Plot the results in a graph, the gradient is the spring constant
• What is the equation for elastic potential energy?


  Ee = 1/2ke²
• What is the equation for Hooke’s law?

  F=ke
• What is the equation for a moment?

  M=fd
• What is the principle of moments?

  When the total clockwise moments equal the total anticlockwise moments the system is in equilibrium and wont move
• How do gears increase the moment?

  By driving a large gear with a smaller one
• How do levers act as force multipliers

  They increase the distance from the pivot
• Why is pressure greater at the bottom of the ocean

  The weight of the water above pushes down on the object
• Why does the air pressure decrease at higher altitudes?

  The air is less dense so the gas particles spread out more so they exert less pressure
• What is the equation for pressure in a column of liquid?

  P=pgh
• What axis is distance on in a distance-time graph

  y-axis
• What axis is time on in a distance-time graph

  x-axis
• What does a flat line mean in a distance time graph?

  the object is stationary
• Average walking speeds

  Walking: 1.5m/s

  Running: 3m/s

  Cycling: 6m/s
• What axis is velocity on in a velocity-time graph?

  y-axis
• What axis is time on in a velocity-time graph?

  x-axis
• What does a flat line show on a velocity-time graph?

  Constant velocity
• What does the area under a velocity-time graph show?

  displacement
• What is the equation for acceleration?

  a=v/t
• What is the typical value for the speed of sound in air?

  330m/s
• What is newton’s first law?

  An object will remain at rest or in motion at a constant speed unless acted upon by a resultant force
• What is newtons second law?

  F=ma
• What is newton’s third law?

  For every action there is an equal and opposite reaction
• Newton’s second law practical

  1. Connect a trolley to a pulley that connects to the end of the table and place the mass on the end of the string to accelerate the trolley
  2. Use photogates to measure the acceleration
  3. Change the force by increasing the mass
  4. Plot F against a, the gradient is the mass
• What is the equation for stopping distance?

  Thinking distance+braking distance
• List five factors that affect the thinking distance

  Speed, distractions, alcohol, drugs, tiredness