Speed & Velocity | Physics for GCSE/IGCSE - Year 11 PDF Download

Speed

• The speed of an object represents the distance it covers in a specific amount of time. It is a scalar quantity, indicating magnitude without direction.
• Speed is a scalar quantity because it only contains a magnitude without a specific direction. For example, if a car is moving at 60 km/hr, the speed is 60 km/hr.
• For objects moving at a constant speed, the speed can be calculated using the formula:
  
• Where:
  • Speed is measured in meters per second (m/s)
  • Distance traveled is measured in meters (m)
  • Time taken is measured in seconds (s)

Average Speed

In scenarios where an object's speed varies, possibly accelerating or decelerating, the average speed is calculated.

• In such cases, the object's speed fluctuates, leading to moments of acceleration and deceleration.
• The formula for determining average speed of an object is utilized:
  
• The formula for average speed (and speed) can be rearranged using the formula triangle provided below.
• The rearrangement of the formulas can be understood with the formula triangle illustrated.
  

How to Use Formula Triangles

Formula triangles are handy tools for rearranging physics equations effectively. Here's how you can use them:

• Cover up the quantity you want to calculate, known as the 'subject' of the equation.
• Observe the positions of the other two quantities:
  • If they are on the same line, they are multiplied.
  • If one quantity is above the other, they are divided - maintain the order for the fraction.
• In a practical scenario, consider calculating speed:
  • Cover 'speed' and you are left with distance and time.
  • Speed is then represented as distance (on the top) divided by time (on the bottom).

How to use formula triangles

Velocity

• Velocity, akin to speed, indicates the rate of motion of an object, but it also specifies the direction of its movement.
  • Speed, being a scalar quantity, solely encompasses magnitude without indicating direction.
• Consequently, velocity qualifies as a vector quantity due to its representation of both magnitude and direction.
  • For instance, velocity could be expressed as '15 m/s south' or '250 mph on a bearing of 030°'.

• Velocity can have a negative value, for instance, when a ball is thrown upwards at 3 m/s, it comes down at -5 m/s if upwards is considered positive. Despite this, their speeds remain 3 m/s and 5 m/s, respectively.
• The equation for velocity closely resembles the equation for speed.
  
• Where
  • v = velocity in meters per second (m/s)
  • s = displacement, measured in meters (m)
  • t = time, measured in seconds (s)
• Velocity is a vector quantity, utilizing displacement, s, instead of distance, which is scalar.