1. Constant Velocity:
- When an object is moving at a constant speed in a straight line, its acceleration is zero. This is because acceleration is the rate of change of velocity, and if the velocity isn't changing, the acceleration is zero.
2. At the Peak of a Trajectory:
- When an object is thrown upwards, it slows down as it goes up due to gravity. At the peak of its trajectory, its velocity momentarily becomes zero before it starts falling back down. Since its velocity is changing, the acceleration is not zero, but it changes its direction at that moment.
3. Balanced Forces:
- If the net force acting on an object is zero, then its acceleration is also zero. This is due to Newton's second law of motion: F = ma (Force = mass x acceleration). If F = 0, then a = 0.
Example:
- A car driving at a constant speed of 60 mph on a straight highway has zero acceleration.
- A ball thrown straight up in the air has zero acceleration at the highest point of its trajectory.
- A book lying on a table has zero acceleration because the force of gravity pulling it down is balanced by the normal force from the table pushing it up.
Key Point: It's important to note that zero acceleration doesn't always mean the object is at rest. It simply means the velocity is not changing. An object can be moving at a constant velocity and still have zero acceleration.
