Force

What is Force??? Force is a push or pull. When one object pushes or pulls on another, the first object is exerting a force on the other. Like velocity, forces are described not only by how strong they are, but also by their direction. The symbols are called vectors. Ex) 10 N in a direction If you push on a door, you exert a force in a different direction than if you pull on the door.

Unbalanced Forces When 2 or more forces are acting on an object, either in the same, or opposite directions, they are added together creating a net force. 3N + 3N = 6N A net force acting on an object is said to be unbalanced. An unbalanced force acting on an object will change the object’s motion by moving it, stopping it, or changing its direction.

Balanced Forces Equal forces acting on an object in opposite directions are called balanced forces. Balanced forces acting on an object will not change the object’s motion. ex) 5N + - 5N = 0 N

Newton’s 1st Law of Motion Inertia - the tendency of an object to resist change in its motion. Ie. An object stays in motion until acted upon by an unbalanced force. An object will remain at rest until acted upon by an unbalanced force. The amount of inertia an object has depends on its mass. The greater the mass the greater the inertia!!!

Newton’s 2nd Law Force, Mass, and Acceleration The net force of an object is equal to the product of its acceleration and its mass. Force = Mass x Acceleration F = M x A The unit: kg x m/s2 Also known as the Newton (N)

F = M x A Don’t forget!!! This formula can also be rearranged using the triangle for another method to find acceleration!! A = Force / Mass

Weight Since weight is a force ( how much gravity pulls on a mass) we can express it according to Newton’s 2nd Law F = M x A Weight = Mass x Acceleration due to gravity And therefore is measured in Newtons

F = M x A Ex) A 52 kg water skier is being pulled by a speed boat. The force causes her to accelerate at 2 m/s2 . Calculate the force that causes this acceleration. Show the formula! Substitute and show work!! Solve with the appropriate units!!!

Solution Force = Mass x Acceleration F = 52kg x 2 m/s2 = F = 104 Newtons = 104 N

Practice Problems What is the force on a 1000 kg elevator accelerating at 2 m/s2 ? 2. How much force is needed to accelerate a 55 kg cart at 15 m/s2 ?

Solution #1 F = M x A F = 1000 kg x 2 m/s2 F = 2000 N F = M x A