Newton’s First Law Inertia The tendency to remain unchanged. An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction… unless acted upon by an unbalanced force. When forces are balanced, no acceleration occurs; as such, an object continues to move at a constant speed or stays at rest.

Compression, Stretch, Shear Forces Directions: There are 6 stations. For each station, make a claim about one of the contact interactions that is happening. Identify the objects that are interacting, what interaction is occurring, and the evidence for the type of interaction. 1. Object suspended by 2 rubber bands 2. Object on a brush being pulled by a string 3. Object suspended between 2 springs 4. Object on a ramp supported on two sides by foam 5. Buggy spinning tires on a brush and pushing against ruler 6. Fan cart pressing into a ball

Forces A force is a concept which represents the existence of physical interactions There are four fundamental forces in nature that govern the physical behavior of the universe: 1. Gravity – acts on objects with mass and at a distance without direct contact 2. Electromagnetic – acts at a distance 3. Strong – keeps nucleus of atoms together 4. Weak – involves with atoms falling apart

Forces A force: Is a push or pull can change the motion of an object Is necessary to make an object accelerate Must involve a contact interaction (except for gravity or electromagnetism)

Forces Gravitational Force (Fg): force of gravity due to attraction between two objects; for us, it is the attraction between all objects and Earth – always a “downward” direction Normal Force (FN): force of a surface that prevents objects from passing through each other; objects MUST be in contact with each other; in a lot of situations, it is in the opposite direction of gravitational force

Forces

Forces Friction (Ff): force of objects as the move across each other or make an effort to move across each other; usually in the opposite direction of motion Tension (FT): force transmitted through a spring, rope, cable, or wire when pulled tight from opposite ends; usually in parallel direction to spring, rope, etc.

Forces Spring (Fs): force of a spring as it is compressed

Forces Forces are measured in Newtons 1 N = 1 kg · m/s2