9.1 The First Condition for Equilibrium

9.1 The First Condition for Equilibrium

• Simple machines are described.

• Explain the forces exerted by muscles.

• A bad posture can cause back strain.

• Skeletal muscles are attached to joints.

• They are normally motionless relative to the Earth.
• Their acceleration is zero because they are motionless.
• Something in common with a car moving at a constant velocity is that it has an acceleration of zero.
• Newton's second law states that the net external force is zero for all stationary and moving objects.
• The forces are balanced.
• They are in equilibrium.

• The study of forces in equilibrium is called statics and it's a special case ofNewton's second law.

• In this chapter, we cover the topic more thoroughly, including consideration of the possible effects of the forces acting on the object.

• Two conditions must be satisfied to achieve equilibrium.
• The topics of the first two sections are about these conditions.

• The net external force on the system must be zero in order to achieve equilibrium.

• The net external force in any direction is zero if the net is zero.
• The net external forces along the x- and y-axes are zero.

• A person is motionless.
• The forces are acting on him.
• The forces are both vertical.

• The car is moving at a constant rate.
• The net external force in any direction is zero.
• The weight of the car is supported by the normal forces and the applied force between the tires and the road is balanced.

• It is not enough for the net external force of a system to be zero.
• The net external force is zero in both situations, but in one case, equilibrium is achieved, whereas in the other, it is not.
• We know that the point at which a force is applied is a factor in determining equilibrium.
• This will be explored in the next section.

• An ice hockey stick is lying flat on ice with two different horizontal forces applied to it.
• The force is balanced by the support of the ice.
• static equilibrium is achieved in this case.