Forces, Movement & Changing Shape Flashcards

Types of Forces

• A force is a push or pull resulting from the interaction between objects.
• Gravitational Force (Weight):
  • Attractive force between objects with mass.
  • Greater mass results in a greater gravitational force.
• Reaction Force:
  • A surface exerts a push force on an object resting on it.
  • Acts at right angles (perpendicular) to the surface.
• Friction:
  • Opposes the motion of an object, causing it to slow down.
  • Occurs when two surfaces move over one another.
• Drag Force:
  • A type of frictional force that occurs when an object moves through a fluid (gas or liquid).
  • Fluid particles collide with the object, slowing it down.
• Air Resistance:
  • A specific type of drag force occurring when an object moves through the air.
  • Air particles collide with the object, slowing it down.
• Thrust:
  • A force produced by an engine that speeds up the motion of an object.
• Upthrust:
  • A fluid exerts an upward-acting push force on an object fully or partially submerged in it.
• Electrostatic Force:
  • Force between two objects with charge.
  • Like charges repel, opposite charges attract.
• Magnetic Force:
  • Force between objects with magnetic poles.
  • Like poles repel, opposite poles attract.
• Tension:
  • Occurs in an object (like a rope or spring) that is stretched when a pull force is exerted on each end.

Effects of Forces

• A force acting on an object can:
  • Change its speed.
  • Change its direction.
  • Change its shape.
• The effects of forces depend on the type of force acting.

Scalar & Vectors

• Scalar Quantities:
  • Quantities that have magnitude but not direction.
  • Examples: mass, distance, speed, energy, volume, density, temperature, power.
• Vector Quantities:
  • Quantities that have both magnitude and direction.
  • Examples: weight, displacement, velocity, force, acceleration, momentum
• Distance vs. Displacement:
  • Distance: Total length of the path traveled (scalar).
  • Displacement: Length and direction of a straight line from start to finish (vector).
• Speed vs. Velocity:
  • Speed: Distance traveled per unit time, regardless of direction (scalar).
  • Velocity: Displacement per unit time, including direction (vector).
• Mass is a scalar quantity; weight is a vector quantity. W = mg
  • Where:
    • W = weight, measured in newtons (N)
    • m = mass, measured in kilograms (kg)
    • g = gravitational field strength, measured in newtons per kilogram (N/kg)

Forces as Vectors

• Vector quantities can be represented by arrows.
  • Length of arrow = magnitude.
  • Direction of arrow = direction.
• Scale should be proportional to relative magnitudes.
• Arrows should be labeled with force names.

Resultant Forces

• A resultant force is a single force describing all forces operating on an object.
• It determines the direction of movement and the net force experienced.
• Forces in the same direction are added; forces in opposite directions are subtracted.
• If forces are equal in size, they are balanced and there is no resultant force.
• Friction:
  • Defined as a force opposing the motion of an object.
  • Acts in the opposite direction to the object's motion.

Unbalanced Forces

• Balanced Forces:
  • Forces cancel each other out, resulting in zero resultant force.
• Unbalanced Forces:
  • Forces do not cancel out completely, resulting in a resultant force.
• Newton's Second Law of Motion:
  • F = m \times a
  • Where:
    • F = resultant force (N)
    • m = mass (kg)
    • a = acceleration (m/s^2)

Weight

• Weight is the force experienced by an object with mass in a gravitational field.
• Weight is a vector quantity; mass is a scalar quantity.
• W = m \times g
  • Where:
    • W = weight (N)
    • m = mass (kg)
    • g = gravitational field strength (N/kg)
• On Earth, g = 10 N/kg

Stopping Distance

• The stopping distance of a car is the total distance traveled during an emergency stop.
• Stopping Distance = Thinking Distance + Braking Distance
• Thinking Distance:
  • Distance traveled while the driver reacts.
  • Affected by speed and reaction time.
• Braking Distance:
  • Distance traveled under braking force.
  • Affected by speed, vehicle mass, and road conditions.

Terminal Velocity

• Terminal velocity is the fastest speed an object can reach when falling.
• Occurs when upward and downward forces are balanced, resulting in zero resultant force.
• Falling objects experience weight and air resistance.
• Air resistance increases with speed until it equals the weight force.
• The weight of the object does not change:W = m \times g
• The initial resultant force is equal to the weight force; the object accelerates downward at maximum acceleration.
• As the object falls, air resistance increases, decreasing the resultant force and acceleration until terminal velocity is reached.

Core Practical: Investigating Force & Extension

• Experiment 1: Investigating force and extension for springs and rubber bands
  • Independent variable: Force (F)
  • Dependent variable: Extension (e)
  • Equipment: Clamp and stand, Ruler, Spring and rubber band, 5 × 100 g masses, 100 g mass hanger, Pointer, G-clamp
  • Method:
    • Align the marker to a value on the ruler with no mass added, and record this initial length of the spring / rubber band
    • Add the 100 g mass hanger onto the spring / rubber band
    • Record the mass (in kg) and position from the ruler now that the spring / rubber band has extended
    • Add another 100 g to the mass hanger
    • Record the new mass and position from the ruler now that the spring / rubber band has extended further
    • Repeat this process until all masses have been added
    • Remove the masses and repeat the entire process again, until it has been carried out a total of three times, and an average length (for each mass attached) is calculated
• Experiment 2:Investigating force and extension for metal wires
  • Independent variable: Force (F)
  • Dependent variable: Extension (e)
  • Equipment: Ruler, Spring, rubber band and metal wire, 5 × 100 g masses, 100 g mass hanger, Tape, Bench pulley, G-clamp & wooden blocks
  • Method:
    • Set up the apparatus so the wire is taut with no masses added
    • Measure the original length of the wire using a metre ruler and mark a reference point with tape preferably near the beginning of the scale eg. at1 cm
    • Record the initial length of the wire to the marker
    • Add a 100 g mass onto the mass hanger
    • Read and record the new reading of the tape marker from the meter ruler now that the metal wire has extended
    • Repeat this process until all masses have been added
    • Remove the masses and repeat the entire process again, until it has been carried out a total of three times, and an average length (for each mass attached) is calculated
• Analysis of results:
  • W = m \times g
  • The extension e of the metal wire is calculated using the equation: e = new marker reading − reference point reading

Hooke's Law

• Hooke's Law states that the extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality.
• Elastic behavior is the ability of a material to recover its original shape after the forces causing the deformation have been removed.
• Elastic Deformation:
  • The object returns to its original shape after the deforming forces are removed.
• Inelastic Deformation:
  • The object does not return to its original shape after the deforming forces are removed.