Forces

Force A force is a push or a pull. When one object pushes or pulls another object, the first object exerts a force on the second object. Force is described by its strength and by the direction in which it acts. If you push on a door, you exert a force in a different direction than if you pull it. Force is measured in Newton’s. This unit is named after the English scientist and mathematician Sir Isaac Newton. 1 Newton = the amount of force needed to accelerate 1 kg mass object at a rate of 1 m/s2.

The larger the mass of an object, the more inertia an object has. Inertia = the resistance to change in motion The law of inertia states that an object at rest will stay at rest and an object in motion will stay in motion until acted upon by an outside force. The larger the mass of an object, the more inertia an object has.

The direction and strength of a force is represented by an arrow The direction and strength of a force is represented by an arrow. The arrow points in the direction of the force. The length of the arrow tells you the strength of the force. The longer the arrow, the greater the force!

Net Force: the combination of all forces acting on an object. The net force determines whether an object moves & in which direction it moves. 5 N in one direction, 15 N in the other direction = 10N net force 5 N in one direction, 15 N in the same direction = 20N net force NET FORCE

But what can we use to help find the net force?! A FREE BODY DIAGRAM! Also known as a force diagram.

Let’s start with something simple, like a book sitting on a table. What forces are acting on that book that keeps it where it is?? The “normal” force = Fn The force of gravity = Fg

mass of an object X the gravitational constant Force of gravity = mass of an object X the gravitational constant m X 9.8 m/s2 The “normal” force is the force that objects exert to prevent solid objects from passing through each other. It is the contact force! This force will be as large as necessary to prevent the surfaces from penetrating each other. The force of gravity = Fg The “normal” force = Fn

Steps for drawing a force diagram: 1. Identify the object you will draw a diagram for.  2. Identify all the forces acting directly on the object. 3. Draw a box to represent the object. 4. Draw a vector (line with an arrow) to represent each force.  Draw it in the direction the force is going, and label it. 5. If the object is stationary or is moving at a constant velocity, the vectors should add up to zero.  If the object is accelerating, the sum of the vectors should produce a vector in the same direction as the acceleration.

Balanced vs. Unbalanced Unbalanced Forces Balanced Forces When there is a net force acting on an object, the force is unbalanced and there is a change in the object’s motion. The unbalanced force can be in the same direction or in the opposite direction. Equal forces acting on one object in opposite directions. The object’s motion does not change. Balanced forces in opposite directions causes zero net force. The forces balance each other out.