Don’t turn to the dark side. Nature of Forces… Don’t turn to the dark side.

What is force? In science a force is a push or a pull. You exert a force on a pencil when you write, on a door when you open it, and on a ball when you kick it. Forces are described by (a) how strong they are and by (b) their direction. A push is a force that acts in the opposite direction of a pull.

Balanced and Unbalanced Forces The forces are considered balanced if they are Equal forces acting on an object in an opposite direction Balanced forces WILL NOT cause motion. The overall or Net Force is zero.

Unbalanced The forces are considered unbalanced if they are unequal forces acting on an object in an opposite direction, or equal or unequal forces acting on the object on the same direction. Unbalanced forces WILL cause motion. The overall or Net Force is NOT zero and is measured in Newtons (N = kg x m/s2).

2 forces in the same direction add together. 7N + 5N = 12N 2 forces in opposite direction subtract from each other. 7N - 5N = 2N

Fnorm = Normal force opposite to gravity (push) Fgrav = Gravitational force (pull) Fapp = Applied force (push or pull) Ffrict = Frictional force resist movement (push)

Describe and draw all the forces involved in the picture of the ball.

If the ball is not moving, the forces are balanced.

Newton’s First Law of Motion (Inertia) In the 1600’s the Italian astronomer, Galileo Galilei suggested that objects that are moving or resting resist change to their motion. This resistance is called “inertia”. In late 1600’s Isaac Newton came up with the 3 basic laws of motion. The first law (Law of Inertia) restates Galileo’s idea.

“ An object at rest will remain at rest and an object that is moving at constant velocity will continue moving at constant velocity unless acted upon by an unbalanced force”. Inertia depends on mass. The greater the mass of an object, the greater its inertia The SI unit of mass is the kilogram (kg) 1 kg = 1,000 grams (g)

Homework: SQ3R 10.1 and Mind Map!!

Remember the Force?? http://www.youtube.com/watch?v=ukbTFgQ4jxs What is Force?

Newton’s Second Law of Motion It relates mass and acceleration to force. It states: “The net force of an object is equal to the product of its acceleration and its mass.” This can be written as: Force = Mass × Acceleration

Then, Acceleration = Force ÷ Mass Mass is in kg Acceleration is in m/s2 Then, force unit is kg.m/s2 = N or 1 N = 1 kg × 1 m/s2 Since F = M × A Then, Acceleration = Force ÷ Mass Acceleration increases when the Force  or the Mass .

Home work! Forces Work Sheet HW Problems: pg 308 #11-15. 18-19. 23-27