Transcript Dynamics!
Dynamics Kinematics: the study of HOW objects move Dynamics: the study of WHY objects move the way they do ◦ Force any push or pull on an object Vector quantity Unit: Newtons (N) 1 N = 1 kgm/s2 ◦ 2 types of Forces Contact Force: involves contact with the object Field Force: force act on the object over a distance…no contact FORCES Contact Forces Applied Force: (Fa): the force a person exerts on an object Frictional Force: (Ff): the force that opposes motion. Always between two surfaces. Acts opposite the direction of an object’s motion Normal Force: (FN): support force. Always perpendicular to the surface Field Force Force due to Gravity: (Fw): the measure of attraction between an object and the center of the earth; the object’s WEIGHT. Always downwards. FREE BODY DIAGRAMS: show all the forces acting on an object; help determine how an object will move. Newton’s 1st Law of Motion The Law of INERTIA ◦ Inertia: the property of an object to resist any change in its motion ◦ This means…an object at rest will stay at rest; an object in motion will stay in motion in a STRAIGHT LINE unless acted upon by an outside force. ◦ Simply put…objects like to keep doing what they’re doing. Mass and Inertia Mass and inertia are DIRECTLY related. ◦ More mass means more inertia. ◦ More inertia means it’s HARDER to change the object’s motion. Net Force To find net force (Fnet) or resultant force, subtract forces in opposite direction. Fnetx = (forces to right) – (forces to the left) Fnety = (forces up) – (forces down) Equilibrium Equilibrium: forces are EQUAL and OPPOSITE ◦ Fnet = 0 N ◦ The object could be: At rest (v = 0 & a = 0) Moving with CONSTANT velocity The object is not ACCELERATING when it is in equilibrium. (But, it can be moving.) Weight vs. Mass Weight (Fw) is a measure of the force due to gravity pulling an object downwards; changes depending on how much gravity there is. ◦ ◦ ◦ ◦ Unit: Newtons (N) Weight = mass x gravity Fw = mg Gravity on earth (g) = 9.81 m/s2 Mass is how much matter an object is made up of; it stays the same no matter where in the universe you are ◦ Unit: kg Newton’s 2nd Law of Motion A net force causes an object to accelerate Acceleration is directly proportional to the net force on the object ◦ The greater the force, the faster the object will accelerate Acceleration is inversely proportional to the mass of the object ◦ The larger the mass, the slower it will accelerate Fnet = ma Newton’s 3rd Law of Motion For every action, there is an equal but opposite reaction. ◦ Forces always occur in pairs. Action Force Reaction Force Force on object A caused by object B A B Force on object B caused by object A Friction Any force that resists the motion of an object ◦ Acts parallel to the surfaces in contact. ◦ Acts in the opposite direction of the object’s motion. Amount of Ff depends on: ◦ The type of materials in contact ◦ The amount of force pressing the surfaces together 2 Types of Friction Static Friction ◦ The friction keeping objects at rest Kinetic Friction ◦ The friction slowing down moving objects **Static friction is always greater than Kinetic friction because it is easier to keep an object moving than it is to start is motion. (Think INERTIA!) **Coefficient of Friction (μ): number describing the type of material. The higher the number, the more friction produced. No UNITS! Falling Objects Objects fall at the same rate if they are falling in a vacuum (no air). Free Fall: Objects fall due to the influence of gravity ◦ Forces Present: Force due to gravity (weight) Force of air resistance (friction) ◦ Terminal Velocity: the fastest an object can fall based on its surface area. Fnet = zero Terminal Velocity As an object falls, it speeds up due to gravity. As the velocity increases, the amount of air hitting the object increases, so friction increases. When the friction is equal to the weight, the net force on the object is zero. No net force means no acceleration. CONSTANT VELOCITY!