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Transcript
Forces May they be with you What is a force? A force is defined as the push or pull on an object. Forces • Some common types of force – Fg = force of gravity – Ff = force of friction – Ft = force of tension – Fn = normal force – Fa = applied force – Fnet = sum of all forces What are the different types of forces? 1. GRAVITY – is a force that pulls down on objects Fg What are the different types of forces? 2. NORMAL– is the force a surface “pushes” into an object FN • If the surface is flat, normal force pushes straight up. (90°) Fg Fg FN • If the surface is angled, the normal force “looks” angled. (but is 90° to the surface) What are the different types of forces? 3. FRICTION– is a force that appears whenever two things are in contact. • No matter which direction • something moves in, • friction pulls it the other way. What are the different types of forces? 4. TENSION– is a pulling force exerted by a string, cable, chain, or rod on another object. • Tension is the opposite of compression. What are the different types of forces? 5. COMPRESSION– a pushing force exerted on another object. for ex; spring FC HOW FORCES “BEHAVE” Forces follow three basic laws called Newton's laws Newton’s Laws of Motion 1st Law of Motion An object at rest will stay at rest unless acted on. An object in motion will stay in motion unless acted on. 1st Law of Motion • “objects will stay doing what they are doing” • The tendency of an object to resist a change in their motion is called Inertia • The more mass an object has the more inertia it has 2nd Law of Motion Force is equal to mass times acceleration 2nd Law of Motion • F=ma • The acceleration of an object depends on the net force acting on an object. • Net force = the addition of all the forces acting on an object 3rd Law of Motion For every action there is an opposite and equal reaction Mass vs. Weight • Mass – how much matter is in something • Weight – how much something is pulled by gravity. Depends on where you are located Force of Friction • Occurs when two objects are in contact with each other. • Coefficient of friction (μ – mu) – μ= friction force/weight • The coefficient of friction depends on whether the object is sliding or not. – If the object is sliding μ is slightly less – This is called sliding or kinetic friction – When friction holds an object at rest we call it static friction.