Vocabulary Term A push or pull. Definition Inertia Newton The resistance of a body to changes to its state of motion. The metric unit of force. Net The sum of all forces acting on an object. Newton s 1 st Law An object at rest will remain at rest unless acted on by an unbalanced force; an object in motion continues with constant speed and direction in a straight line unless acted on by an unbalanced force. Newton s 2 nd Law = mass x acceleration Newton s 3 rd Law For every action, there is an equal and opposite reaction. 1 Page
Newton s 1 st Law of Motion Newton s 1 st Law of motion Main Ideas is also know as the law of Inertia Definition of inertia: An object at rest will remain at rest an object in motion continues with constant speed and direction in a straight line The resistance of a body to changes to its state of motion. Unless acted upon by an A push or pull. Applying Newton s 1 st Law of motion Explain according to Newton s 1 st law of motion what would happen to the person in the car NEWTON S below if they FIRST crashed LAW into OF the MOTION wall using (aka: the terms ) inertia, state of motion, and unbalanced States: force. An The Object person and the car both have inertia, thus will continue in motion unless an unbalanced force acts on them. When the car crashes into the wall and unbalanced force acts upon the car to change its state of motion, the car stops; however, there is no unbalanced force acting on the person so they continue moving forward. 2 Page
Inertia is the property of an object that resists changes in motion. Class Work 1. Which has more inertia a bowling ball or a golf ball? Bowling Ball 2. Objects with more mass have more inertia and are more resistant to changes in their motion. 3. Mac and Tosh are arguing in the cafeteria. Mac says that if he flings the Jell-O with a greater speed it will have a greater inertia. Tosh argues that inertia does not depend upon speed, but rather upon mass. Who do you agree with? Explain why. Tosh because inertia depends on mass and mass alone. 4. Fred spends most Sunday afternoons at rest on the sofa, watching pro football games and consuming large quantities of food. What effect (if any) does this practice have upon his inertia? Explain. Increases inertia. 3 Page
Notes Newton s Second Law John and Joe have a grocery cart race. John pushes a loaded grocery cart; Joe pushes an empty grocery cart. Joe wins the race. Why? Joes has less mass to push, thus can accelerate his cart faster. John Joe Joe and his little brother Junior have a grocery cart race. Joe wins the race. Why? Joe can push with a greater force than junior can. Joe Junior 1. When a grocery cart is pushed by a person, a(n) unbalanced force acts on the cart and the cart accelerates. 4 Page
2. The acceleration of an object is directly proportional to the net force acting on it. This means that, as the net force acting on the object increases, the acceleration of the object increases. Newton s 2 nd Law of Motion states: The acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to the object s mass. 2 nd law abbreviated using symbols: F = ma F = sum of the forces m = mass a = acceleration Newton s 2 nd law relates the net force on an object, the mass of the object, and acceleration. It states that the stronger the net force on an object, the faster the object will accelerate. If twice the net force is applied, the acceleration will be twice as great. The acceleration of an object is directly proportional to the net applied force and inversely proportional to the mass. (in other words if the force increases, the acceleration increases and if the mass increases the acceleration decreases.) F a m NEWTON S 2 ND LAW Formula Want to find What you know A = F/m acceleration (a) force (F) and mass (m) F = ma force (F) acceleration (a) and mass (m) m = F/A mass (m) acceleration (a) and force (F) 5 Page
Newton s 2 nd Law Formula F = ma Net No Acceleration dd forces Subtract forces Net force is Zero. Objects are at rest or moving with constant speed. ame Direction Opposite Direction 6 Page
NEWTON S SECOND LAW Formula Want to find What you know acceleration=/mass acceleration force (F) and mass (m) (a) =mass x acceleration force (F) acceleration (a) and mass (m) Mass = / acceleration mass (m) acceleration (a) and force (F) a F m Class Work 1. A 1650 kg car accelerates at a rate of 4.0 m/s 2. How much force is the car's engine producing? m=1650 kg =(1650 kg) x (4m/s 2 ) a=4 m/s 2 F=ma =6600 N 2. A tennis ball, 0.314 kg, is accelerated at a rate of 164 m/s 2 when hit by a professional tennis player. What force does the player's tennis racket exert on the ball? m=0.314 kg a=164 m/s 2 F=ma =(0.314 kg) x (164m/s 2 ) =51.5 N 3. A crate is dragged across an ice covered lake. The box accelerates at 0.08 m/s 2 and is pulled by a 47 N force. What is the mass of the box? Mass F=47 N a=0.08 m/s 2 m=f/a = 47 N / 0.08 m/s 2 =587.5 kg Group Work 1. What is the rate of acceleration of a 2,000-kilogram truck if a force of 4,200 N is used to make it start moving forward? 7 Page
Acceleration F=4200 N m=2000 kg a=f/m 2.1 m/s 2 2. What is the acceleration of a 0.30 kilogram ball that is hit with a force of 25 N? Acceleration F=25 N a=f/m 83.33 m/s 2 m=0.30 kg 3. How much force is needed to accelerate a 68 kilogram-skier at a rate of 1.2 m/sec2? m=68 kg 81.6 N a=1.2 m/s 2 F=ma 4. What is the mass of an object that requires a force of 30 N to accelerate at a rate of 5 m/sec2? Mass F=30 N 6 kg a=5 m/s 2 m=f/a 5. What is the force on a 1,000 kilogram-elevator that is falling freely under the acceleration of gravity only? m=1000 kg 9800 N a=9.8 m/s 2 F=ma 6. What is the mass of an object that needs a force of 4,500 N to accelerate it at a rate of 5 m/sec2? Mass F=4500 N 900 kg a=5 m/s 2 m=f/a 7. What is the acceleration of a 6.4 kilogram bowling ball if a force of 12 N is applied to it and it experiences a 4-N frictional force? Acceleration m=6.4 kg a=f/a 1.25 m/s 2 F=12 N 8 Page
HomeWork (10 points) 1. What is the rate of acceleration of a 1,000-kilogram truck if a force of 4,200 N is used to make it start moving forward? Acceleration m=1000 kg a=f/m 4.2 m/s 2 F=4200 N 2. What is the acceleration of a 0.30 kilogram ball that is hit with a force of 50 N? Acceleration m=0.30 kg a=f/m 166.67 m/s 2 F=50 N 3. How much force is needed to accelerate a 68 kilogram-skier at a rate of 1.2 m/sec 2? m=68 kg 81.6 N a=1.2 m/s 2 F=ma 4. What is the mass of an object that requires a force of 30 N to accelerate at a rate of 5 m/sec2? Mass F=30 N m=f/a 6g k a=5 m/s 2 5. What is the mass of an object that needs a force of 4,500 N to accelerate it at a rate of 5 m/sec 2? Mass F=4500 N m=f/a 900 kg a=5 m/s 2 9 Page
Newton s 3 rd Law ACTION REACTION states that For every action there is an equal and opposite reaction. Wall hits fist Bug hits windshield s are equal in s are opposite in magnitude direction Ball hits bat. Bar pushes downward. 10 Page