McDonalds Flashcards
A object falls. Describe and explain its motion.
At the start, the only force on it is gravity. So, the net force is downwards. So, the velocity downwards increases and it speeds up. As it speeds up, friction increases, opposing the velocity. So, the net force is still downwards, but not as large. So there is still an acceleration downwards, but not as large. So, its velocity downwards increases and it speeds up, but not by as much. Eventually, the speed is so large that friction is equal but opposite to the weight. So, the net force is zero. So, the acceleration is zero, so the object moves at constant speed. This is called terminal velocity.
A driver places his foot on the accelerator pedal and does not let go. Describe and explain the motion.
At the start, the only force on it is the driving force. So, the net force is forwards. So, the velocity forwards increases and it speeds up. As it speeds up, friction increases, opposing the velocity. So, the net force is still forwards, but not as large. So there is still an acceleration forwards, but not as large. So, its velocity forwards increases and it speeds up, but not by as much. Eventually, the speed is so large that friction is equal but opposite to the driving force. So, the net force is zero. So, the acceleration is zero, so the object moves at constant speed. This is called terminal velocity.
