Final answer:
No net force is indicated when an object moves straight up at constant speed; this is consistent with Newton's first law, which states that an object will remain at rest or in uniform motion unless acted upon by an external force.
Step-by-step explanation:
Indicators that there is no net force on an object align with Newton's first law of motion which states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. Therefore, an object experiencing no net force may either be at rest or moving with constant velocity in a straight line. The options presented in the question can be analyzed as follows:
- Its speed is changing - this implies acceleration due to a net force.
- Its velocity is changing - this also implies acceleration.
- It is moving in a curved path - uniform circular motion requires a centripetal force, thus a net force exists.
- It moves straight up at constant speed - this suggests a balance of forces (gravity and an upward force), hence no net force as they cancel each other out.
- It is accelerating - acceleration is a clear sign of a net force according to Newton's second law.
Therefore, the correct indication that there is no net force on an object is when it moves straight up at constant speed. For an object to be in a condition of no net force, its state of motion should not be changing, meaning it should not be accelerating and should maintain its velocity if it's already in motion.