Physics - forces and motion

• How is speed defined?

  Speed is defined as the distance travelled per unit time.

  
• What happens if the speed of something is changing?

  If the speed of something is changing, it is accelerating.
• What is the acceleration of free fall near to the Earth?

  The acceleration of free fall near to the Earth is constant.
• What is the formula for average speed?


  $\text{average speed} =$$\frac{\text{total distance}}{\text{total time}}$
• How is velocity defined?

  Velocity is the speed in a given direction.

  
• What is acceleration?


  Acceleration is the change in velocity per unit time.
• What is the formula for acceleration?


  $a =$$\frac{\text{change in velocity}}{\text{time taken}}$
• What does the equation $v^2 =$$u^2 +$$2as$ represent?


  This equation relates the final speed, initial speed, acceleration, and distance travelled.
• In what units is distance measured?

  Distance is measured in metres (m).
• In what units is time measured?

  Time is measured in seconds (s).
• In what units are speed and velocity measured?

  Speed and velocity are measured in metres per second (m/s).
• In what units is acceleration measured?

  Acceleration is measured in metres per second squared (m/s²).
• What does a distance-time graph indicate?

  • The gradient represents velocity.
  • A negative gradient indicates returning to the starting point.
  • A horizontal line means the object is stationary.
  • If the distance is zero, the object is back at the starting point.
  • A curved line indicates changing velocity and acceleration.

  
• What does a velocity-time graph indicate?

  • The gradient represents acceleration.
  • A negative gradient indicates deceleration.
  • If the speed is zero, the object is at rest.
  • A horizontal line means constant speed.
  • The area under the line represents the distance travelled.
  • A curved line indicates changing acceleration.

  
• What is the difference between a vector and a scalar?

  A vector has magnitude and direction, while a scalar has just a magnitude.
• What are examples of scalars and vectors?

  Scalars:

  • Distance
  • Speed
  • Time
  • Energy

  
  

  Vectors:

  • Displacement
  • Velocity
  • Acceleration
  • Force
• What can forces change in a body?

  Forces can change the speed, shape, or direction of a body.
• In what units are forces measured?

  Forces are measured in Newtons (N).
• What is friction?

  Friction is a force between two surfaces that impedes motion and results in heating.
• How do you find the resultant of two or more forces acting along the same line?


  They should be added together if in the same direction and subtracted if in the opposite direction.
• What does Newton's first law state?

  Newton's first law states that an object has a constant velocity unless acted on by a resultant force.
• What does Newton's second law state?

  Newton's second law states that $F =$$ma$, where force equals mass times acceleration.
• What does Newton's third law state?

  Newton's third law states that every action force has an equal and opposite reaction force.
• What is mass a measure of?

  Mass is a measure of how much matter is in an object.
• In what units is mass measured?

  Mass is measured in kilograms (kg).
• What is weight?


  Weight is a gravitational force, the effect of a gravitational field on a mass.
• What is the formula for weight?

  $w =$$mg$, where $w$ is weight, $m$ is mass, and $g$ is gravitational field strength.
• What is the gravitational field strength on Earth?

  The gravitational field strength on Earth is 10 N/kg.
• Where does the weight of an object act?

  The weight of an object acts through its centre of gravity.
• What happens to a body falling in a uniform gravitational field?

  • Initially, there is no air resistance; only weight acts on it.
  • As it falls, it accelerates, increasing speed and air resistance.
  • Resultant force downwards decreases as air resistance increases.
  • Acceleration decreases until air resistance equals weight.
  • Terminal velocity is reached when there is no resultant force.
• What is thinking distance in driving?


  The thinking distance is the distance travelled from realizing the need to brake to actually pressing the brakes.
• What factors increase thinking distance?

  • Greater speed
  • Slower reaction time due to alcohol, tiredness, or distractions
  • Caffeine can reduce thinking distance.
• What is braking distance?

  The braking distance is the distance travelled from pressing the brakes to the vehicle coming to a stop.
• What factors increase braking distance?

  • Greater speed or mass
  • Poor road conditions (icy, wet)
  • Poor car conditions (worn tires, worn brake pads)
• What is stopping distance?

  • Stopping distance = thinking distance + braking distance.
• What does Hooke's law state?

  Hooke's law states that $F =$$kx$, where $F$ is the force applied to the spring, $k$ is the spring constant, and $x$ is the extension.
• What does a linear force-extension graph indicate?

  • Elastic deformation follows Hooke's law.
  • The limit of proportionality is where it stops being linear.
  • The gradient represents the spring constant, $k$.

  
• What does a non-linear force-extension graph indicate?

  • Deformation does not follow Hooke's law.
  • After this region, the material will fracture.

  
• What is the moment of a force?

  The moment of a force is a measure of its turning effect, measured in Newton metres (Nm).
• What is the formula for moment?


  $\text{moment} =$$\text{force} \times \text{perpendicular distance from the pivot}$