Mechanics - Laws of Motion - SS2 Physics Past Questions and Answers - page 5

Newton's first law, also known as the law of inertia, explains why seat belts are important in car safety. When a car suddenly stops or changes direction, an unrestrained object, including the occupants, tends to continue moving with its original velocity. Seat belts apply a restraining force to prevent this, in accordance with Newton's first law. Additionally, airbags utilise Newton's second law by rapidly inflating and providing a force opposite to the direction of the occupant's motion, reducing the impact force during a collision.

Newton's second law plays a crucial role in the design and operation of elevators. The upward acceleration of an elevator is determined by the net force acting on it, which is the difference between the gravitational force acting downward and the upward force provided by the elevator's motor. By adjusting the motor's force, the elevator can be made to move up, down, or remain stationary. Newton's third law also comes into play as the elevator exerts an equal and opposite force on the passengers when it starts or stops.

Newton's third law is the foundation of rocket propulsion. According to this law, for every action, there is an equal and opposite reaction. In the case of a rocket, burning fuel inside the rocket's engine produces a high-speed stream of gases as the action. As a result, the rocket experiences a reaction force in the opposite direction, propelling it forward. Newton's second law is also involved in determining the acceleration of the rocket based on the mass of the rocket and the force produced by the engine.

Newton's laws are crucial in the construction and stability of bridges. For example, when designing a suspension bridge, engineers consider the tension forces in the cables that support the bridge deck. These tension forces must be carefully balanced to ensure the bridge remains stable. Newton's second law helps determine the distribution of these forces and ensures that the bridge can support the weight of vehicles and other loads. Additionally, Newton's third law comes into play as the bridge exerts an equal and opposite reaction force on any object, such as a vehicle, that applies a force on it.