If the object has a constant velocity, that means that the net acceleration must be zero.

In conjunction with Newton's second law, we can see that the net force is also zero. If there is no net acceleration, then there is no net force.

Since Franklin is lifting the weight vertically, that means there will be two force acting upon the weight: his lifting force and gravity. The net force will be equal to the sum of the forces acting on the weight.

Since we just proved that the net force will equal zero, we can say .

We know the mass of the weight and we know the acceleration, so we can solve for the lifting force.

If the object has a constant velocity, that means that the net acceleration must be zero.

In conjunction with Newton's second law, we can see that the net force is also zero. If there is no net acceleration, then there is no net force.

Since Franklin is lifting the weight vertically, that means there will be two force acting upon the weight: his lifting force and gravity. The net force will be equal to the sum of the forces acting on the weight.

Since we just proved that the net force will equal zero, we can say .

We know the mass of the weight and we know the acceleration, so we can solve for the lifting force.

Remember, in a force diagram, forces come from the center of the object. The force of gravity will always be straight down from the center of the object.

In this diagram, W is pointed directly downward.

Remember, in a force diagram, forces come from the center of the object. The force of gravity will always be straight down from the center of the object.

In this diagram, W is pointed directly downward.

The force due to friction will always be parallel to the surface upon which the object is traveling. It will come directly from the center of the object, and be pointed in the opposite direction to the motion of the object.

In this diagram, V is pointed parallel to the surface and opposite to the direction of motion.

The force due to friction will always be parallel to the surface upon which the object is traveling. It will come directly from the center of the object, and be pointed in the opposite direction to the motion of the object.

In this diagram, V is pointed parallel to the surface and opposite to the direction of motion.

The normal force is always perpendicular to the surface on which the object is placed, and is pointed away from said surface.

In this diagram, Z is the only force that is perpendicular to the surface and in the upward direction. This force must counteract the vertical force of gravity, which will be perpendicular to the surface in the downward direction (Y).

The normal force is always perpendicular to the surface on which the object is placed, and is pointed away from said surface.

In this diagram, Z is the only force that is perpendicular to the surface and in the upward direction. This force must counteract the vertical force of gravity, which will be perpendicular to the surface in the downward direction (Y).

In this diagram, V represents the force due to friction. The equation for the force due to friction is , where is the coefficient of friction.

In this case, Z represents the normal force. We can re-write the equation for friction:

Z can be re-written in terms of the angle, but will always need to be multiplied by the coefficient of friction in order to give an equation for V.

The other equations are true.

- X and Y form a right angle, so the Pythagorean theorem applies.

- Z is the normal force, which is, by definition, equal and opposite the vertical force of gravity.

- W is the total force of gravity, which will be equal to the mass times the acceleration of gravity.

- the triangle formed by W, X, and Y is similar to the triangle formed by the surface, Q, and P, meaning that these angles must be equal.

In this diagram, V represents the force due to friction. The equation for the force due to friction is , where is the coefficient of friction.

In this case, Z represents the normal force. We can re-write the equation for friction:

Z can be re-written in terms of the angle, but will always need to be multiplied by the coefficient of friction in order to give an equation for V.

The other equations are true.

- X and Y form a right angle, so the Pythagorean theorem applies.

- Z is the normal force, which is, by definition, equal and opposite the vertical force of gravity.

- W is the total force of gravity, which will be equal to the mass times the acceleration of gravity.

- the triangle formed by W, X, and Y is similar to the triangle formed by the surface, Q, and P, meaning that these angles must be equal.