Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Newton’s Second law Force and Acceleration How are forces related to motion? • What is a force????? • The unit of force is the Newton (N). • 1 kg of mass exerts about 10 N of force. Forces... • Can cause a change in an object’s state of motion… • A force can increase or decrease speed OR change the direction of an object. In other words… Force causes acceleration! TYPES OF FORCES • Balanced forces… • Unbalanced forces... Balanced Forces • Equal in size • Condition of equilibrium • Opposite in direction • Net force = 0 • They cancel • Thus, no each other out acceleration! An example... When you stand on the floor, your weight pushes down while the floor pushes up... Another example… Force the road Force the tires applies to the tires apply to the road One more... The wall pushes Dave pushes on on Dave the wall Unbalanced Forces... • Can be • Net force = 0 unequal • Causes • Do not cancel acceleration! • No • Examples... equilibrium Here we go... Force the tires exert on the road Force the road exerts on the tires One more... Tires pushing Curve pushing against the against the curve tires Newton’s nd 2 Law • Acceleration is proportional to force… –The more the force… –The less the force... Newton’s nd 2 Law • Acceleration is proportional to mass… –The more the mass… –The less the mass... Put it all together... A = F/m Newton’s Second Law An object will accelerate in the direction you push it…the harder the push, the greater the acceleration, the bigger the mass, the less the acceleration will be. The Equation... F = ma Applications... • Weight : the force due to gravity –W = mg : g = 9.8 m/s2 • Air friction… –Please read Ch. 5! What are the effects of air friction while falling? In free fall, objects are being accelerated by gravity. • The force due to gravity is weight. F = m a Wt = m g EXAMPLE • What is the weight of a 100 kg sky diver? • m = 100 kg • g = 10 m/s2 • Wt = ? EXAMPLE • Wt = 100 kg x 10 m/s2 • Wt = 1000 N Air Friction 1. Is also known as Air Resistance Air Friction 2. The amount of air resistance will increase as a. The speed increases b. The area of surface increases Air Friction 3. Opposes gravity • Friction always goes against motion Air Friction • Net Force = weight - air friction • EXAMPLE…... What is the net force acting on a 150 kg sky diver with 500 N of air resistance? m = 150 kg 2 g = 10 m/s Wt = 1500 N 1500 N Wt = 1500 N Air resistance = 500N Net Force = 1500N - 500N 500 N • Net Force = 1000 N • If the object falls fast enough, the force of air resistance will equal the force of gravity. 1500 N • Forces are balanced – No acceleration 1500 N • Falling speed will stop increasing The fastest speed when falling is called terminal velocity. Terminal velocity is greatest when: • Large weight (more downward force) • Small surface area (less resistance) PRESSURE • Amount of force per unit area. • P = force / area •P=F/A PRESSURE IS MEASURED IN PASCALS • 1 Pa = 1 N/m2 • Very small pressure • Sometimes use kilopascals (kPa) Pressures is greater when….. • The force is bigger. • The area is smaller. Which exerts the greatest pressure? OR •Why do objects fall at the same rate (no air resistance)? Acceleration is a ratio. •F / M = F / M • The ratio of force to mass is constant and equals gravity.