Given:
5 different situations.
To find:
To determine if the friction is acting as a friend or a foe.
Step-by-step explanation:
Friction is the force that opposes the motion of an object. Thus it is always directed in the direction opposite to the direction of motion of the object.
1. In this situation, your kinetic energy is transferred into heat through frictional force and hence you get scratches. Thus in this situation, the friction is acting as a foe.
2. To turn the bike around a sharp curve, the centripetal force is required to keep the bike on the track. The frictional force provides the necessary centripetal force. Thus without friction, the bike would slide off the track and the rider will be injured. Thus in this case the friction is acting as a friend.
3. When you are racing down, the friction force acts in the direction opposite to the direction you are racing and thus helping you to move forward without slipping. Thus the friction is acting as a friend in this case.
4. As friction is acting in the direction opposite to the direction you are pushing the desk, some of the work you are doing will be wasted to overcome the frictional force. Thus, in this case, the friction is acting as a foe.
5. As soon as you see the possum, you apply the brake. The frictional force between the tires and the road helps you to come to stop by acting in the direction opposite to the direction of motion of the car. Thus in this case the friction is acting as a friend.
Final answer.
1. Friction is a foe.
2. Friction is a friend.
3. Friction is a friend.
4. Friction is a foe.
5. Friction is a friend.