What is the difference between speed and velocity? between velocity and acceleration?

A scalar quantity is a physical measurement that only has a magnitude (size or amount) but no direction. This means it tells us 'how much' of something there is but does not tell us 'which way.' Common examples of scalar quantities include:
- Speed
- Distance
- Mass
Speed is a great example to think about. If you say a car travels at 60 km/h, you only know how fast it is going, not where it is going. Scalars are straightforward and often easier to handle in calculations. Remember, with scalars, direction doesn't matter; only the amount counts.

Unlike scalar quantities, vector quantities have both magnitude and direction. They tell us not only 'how much' but also 'which way.' Typical examples of vector quantities include:
- Velocity
- Displacement
- Force
Velocity is an important concept to understand here. If a car is moving at 60 km/h to the east, you're dealing with a vector. Both the speed (60 km/h) and the direction (east) are specified. Vector quantities are crucial when you need to understand how objects move in a specific direction, interact, or balance out in equations. When working with vectors, it's vital to consider both the amount and the direction.

Acceleration is all about how quickly an object's velocity changes. It's a vector quantity, meaning it has both a magnitude and a direction. Acceleration can happen due to changes in speed, direction, or both. There are a few key points to remember about acceleration:
- It's measured in units of velocity per time, like meters per second squared (m/s²).
- It can be positive (speeding up) or negative (slowing down), which is often called deceleration.
- Forces cause acceleration; when you apply force to an object, you change its velocity.
Think of a car accelerating from 0 to 60 km/h to the east in 10 seconds. Here, the car's velocity changes from zero to 60 km/h eastward, meaning it has an eastward acceleration during this time. Newton's Second Law of Motion, which states that Force equals Mass times Acceleration (F = ma), explains why understanding acceleration is so important in physics. It helps us predict and understand the behavior of moving objects.