Summary
Highlights
Normal force is exerted by a surface to prevent an object from falling through it. In a simple scenario where only gravity acts downwards, the normal force is equal to the force of gravity. For example, a 5 kg object would have a normal force of 49 Newtons (5 kg * 9.8 m/s^2).
When an additional force is applied at an upward angle, its vertical component helps to counteract gravity. If a 10 Newton force is applied at a 30-degree angle, its vertical component (y-component) is 5 Newtons (sin 30 * 10). In this case, the normal force will be reduced: Normal Force = Gravity - Y-component of applied force. So, 49 N - 5 N = 44 N. The normal force works less because the applied force is partially lifting the object.
If a force is applied at a downward angle, its vertical component adds to the effect of gravity, pushing the object more into the surface. Using the same 10 Newton force at a 30-degree angle, the downward y-component is still 5 Newtons. Here, the normal force must work harder: Normal Force = Gravity + Y-component of applied force. So, 49 N + 5 N = 54 N.
In summary, the normal force equals gravity when only gravity is acting. It is gravity minus the y-component of the applied force if the force has an upward vertical component. It is gravity plus the y-component of the applied force if the force has a downward vertical component.
Friction is directly proportional to normal force (Friction = coefficient of friction * Normal Force). When the normal force decreases (due to an upward angled force), friction also decreases. This is because the object is slightly lifted, reducing the microscopic interaction with the surface. Conversely, when the normal force increases (due to a downward angled force), friction increases as the object is pushed more firmly into the surface, increasing resistance.