Understanding Acceleration in Middle School Physics | Khan Academy

Defining Acceleration

• 💡 Acceleration is defined as the change in an object's velocity.
• ⚡ This change can occur if the object's speed or direction (or both) are changing.
• 🎯 If an object's speed and direction remain constant, its velocity is constant, and its acceleration is zero.

Speeding Up vs. Slowing Down

• 🚀 When an object is speeding up, its acceleration is in the same direction as its velocity.
• ⚠️ Conversely, when an object is slowing down, its acceleration is in the opposite direction of its velocity.
• 📈 The rate at which velocity changes is a measure of acceleration; for example, a car going from 0 to 60 mph in 2.3 seconds indicates how quickly its velocity changed.

Direction of Acceleration

• ⬆️ A ball thrown upwards slows down, meaning its velocity is upwards, but its acceleration is downwards.
• ⬅️ A bike moving left and speeding up has its acceleration also directed to the left, in the same direction as its velocity.
• ✈️ An airplane cruising at a constant velocity has zero acceleration because its velocity is not changing.

Acceleration and Constant Speed

• 🚗 An object can have constant speed but still be accelerating if its direction is changing, such as a car moving in a circle.
• 🔄 In circular motion, the speed might be constant, but the continuously changing direction means the velocity is changing, thus resulting in acceleration.