A car is at rest on a horizontal road. What is the value of the frictional force? Explain your answer.

A bison stands at rest on the horizontal ground. What is the value of the frictional force? Explain.

The normal force always has a direction perpendicular to the surface that is causing the normal force. Is the normal force on your feet always directed straight up? If not, give an example of when it isn't.

Thank you so much!

To answer your questions:

1. A car at rest on a horizontal road experiences static friction. The value of the frictional force can be calculated using the equation: Fs ≤ μs * N, where Fs is the static friction force, μs is the coefficient of static friction, and N is the normal force. Since the car is at rest, the static friction force must be equal to zero, as it opposes any potential motion. The value of the frictional force is therefore zero.

2. Similar to the car example, a bison at rest on the horizontal ground also experiences static friction. The value of the frictional force can be calculated using the same equation: Fs ≤ μs * N. As the bison is also at rest, the static friction force must be equal to zero, resulting in the frictional force having a value of zero.

3. While it is true that the normal force on your feet is typically directed straight up, there can be exceptions. One such example is when you are standing on an inclined plane. In this case, the normal force is still perpendicular to the surface of the plane, but it is no longer directed straight up. Instead, it is directed perpendicular to the plane, adjusting its direction in response to the incline.

To determine the value of the frictional force, we first need to understand the factors that affect it. Friction is the force that opposes motion when two surfaces are in contact with each other. Its strength depends on two main factors: the nature of the surfaces in contact and the normal force applied on the object.

1. Car at rest:
When a car is at rest on a horizontal road, the frictional force acting on it is known as static friction. This force prevents the car from moving and is equal in magnitude and opposite in direction to any applied force trying to push or pull the car. Since the car is not moving, the static friction force exactly balances the applied force to keep the car stationary.

2. Bison at rest:
Similar to the car at rest, when a bison is standing still on a horizontal surface, the frictional force acting on it is static friction. The static friction force opposes any external force acting on the bison, keeping it from moving.

3. Normal force and direction:
The normal force is the force exerted by a surface to support the weight of an object resting on it. It always acts perpendicular to the surface at the point of contact. In most situations, the normal force is directed straight up because gravity pulls the object downward, causing the surface to exert an equal and opposite force.

However, there are instances when the normal force is not directed straight up. For example, consider standing on a sloped surface. In this case, the normal force will be directed perpendicular to the sloped surface, not straight up.

In summary:
- The frictional force for a car or a bison at rest on a horizontal surface is static friction.
- The value of the static friction force depends on the applied force and is adjusted to prevent motion.
- The normal force is typically directed straight up but can vary in direction depending on the orientation of the surface.