Chapter 4 Newtons Laws Sir Isaac Newton Came

Chapter 4 Newton’s Laws

Sir Isaac Newton Came up with three laws of motion l Also wrote the Law of Universal Gravitation l

Newton’s First Law of Motion 1 st Law: An object at rest will stay at rest and an object in motion will stay in motion UNLESS acted upon by an outside force. l Only an unbalanced force can cause motion to change l Remember, a force is a push or pull l

First Law Cont. If a car traveling at 65 km/hr suddenly stops, why would you fly forward? l Why is it important to wear a seatbelt? l An astronaut out in space throws a ball. What would happen to the ball? l What are the unbalanced forces that stop the motion of the matchbox car? l

First Law Cont. The first law is also known as the law of inertia. l Inertia: the tendency of an object to resist change in motion. l The more mass an object has, the more inertia it has. l

First Law Cont. Which will change its velocity more easily: a 12 pound bowling ball traveling at 2 m/s or a ping pong ball traveling at 2 m/s? l Which has more intertia: l

Newton’s Second Law l 2 nd Law: the acceleration of an object is in the same direction as the net force on the object and that acceleration equals the net force divided by the mass.

Second Law Cont. Objects with more mass take more force to accelerate. l The smaller the mass, the greater the rate of acceleration. l The greater the unbalanced force acting on an object, the greater the acceleration. l

Second Law Cont. l The second law can be shown in these formulas: l Force = Mass * Acceleration or F = M * A l. M=F/A l. A=F/M

Second Law Practice l Units: Force is Newtons, Mass is kilograms, and Acceleration is m/s 2 l How much force is needed to move a 900 kg object 32 m/s 2?

Second Law Practice Cont. l What is a car’s mass if the net force is 3000 N and has an acceleration of 2 m/s 2? l If the mass of a helicopter is 4500 kg and the net force is 18000 N, what is its acceleration?

Newton’s Third Law 3 rd Law: when one object exerts a force on a second object, the second object exerts a force on the first object equal in strength but opposite in direction. l Put simply, for every action, there is an equal and opposite reaction. l

Third Law Examples l Your foot pushes on the floor with 50 N. The floor pushes back in the opposite direction with 50 N.

Momentum: property of a moving object that equals its mass times velocity l Think: how much force is needed to change an object’s motion? l l Which has more momentum: a 10 lb bowling ball moving at 2 m/s or a 1 lb softball moving at 1 m/s?

Momentum Cont. Momentum = Mass * Velocity l This equation is shown as P = M * V l Units: Mass is kg, Velocity is m/s and Momentum is kg*m/s l

Momentum Practice l A car with a mass of 1300 kg travels at a speed of 28 m/s. What is the momentum? l A baseball travels at 40 m/s and has a mass of. 15 kg. Momentum?

Law of Conservation of Momentum l The Law of Conservation of Momentum states that when objects exert forces only on each other, the total amount of momentum stays the same.

Law of Conservation of Momentum Examples

Law of Conservation of Momentum Examples

Law of Conservation of Momentum Examples

Law of Conservation of Momentum Examples

4. 1 Motion Law Analysis: Hr___ Name_______ Date__ Copy & explain in sentences. Show all work. 1. What forces act on moving objects? 2. Can forces act on objects at rest? 3. What is the force on a 3 kg book if it accelerates at 1. 5 m/s/s? 4. What is total mass of you and skateboard pushing at 30 N & accelerating at 0. 5 m/s/s

Gravity 4 -2

What is Gravity? Gravity is the attractive force between two objects. l All objects made of matter have gravitational attraction. l The force of gravity is affected by two forces: l l The mass of objects l The distance between the objects

Mass and Distance l The more mass an object has, the greater the gravitational pull. l Ex: Gas giants have more moons around them than the smaller, inner planets. l The closer one object is to another, the stronger the gravitational pull. l Ex: Sun and moon both have a gravitational pull on Earth, but Earth’s is stronger since we are closer to it.

Newton’s Law of Universal Gravitation: a mathematical calculation between mass and the distance between two objects. l F = G m 1 m 2 D 2 Force = gravitational acceleration * mass of the first object * the mass of the second object divided by the distance squared. l

L. U. G. Cont. This equation simply states the strength of gravity depends on the masses of objects and the distances between them. l The gravitational acceleration of objects close to Earth’s surface is 9. 8 m/s 2 l

Gravitational Acceleration If a bowling ball and a tennis ball are dropped from the same height in a vacuum (no air resistance), then both hit the ground at the same time. l WHY? ? ? l All objects in the absence of air resistance accelerate at 9. 8 m/s 2 close to Earth’s surface l

l What two factors keep planets and moons in orbit? l GRAVITY and INERTIA

Weight VS Mass l Weight: a measurement of the gravitational pull on an object l Mass: the amount of matter in an object

Weight VS Mass Cont. l Why are you weightless in outer space, yet still have the same mass? l On which planet would you weigh the most?

Projectile Motion Projectile: any object that is thrown or shot through the air l Why do projectiles fall in a curve? l l Due to CENTRIPETAL ACCELERATION, an object will accelerate on a curved path. As velocity changes, the object will have a curved path.

Centripetal Force: the net force applied to an object traveling in a circular path. l DEMO: the bucket and the dime l

4. 2 Gravity Analysis: Date_____ Name_________ Hr_ Copy & explain in sentences. Show all work. 1. Describe how gravity depends on masses and distances between two objects. 2. What causes projectile paths to curve? 3. What is weight of a 75 kg TV on Earth? 4. What is acceleration of gravity on Mars if a 60 kg person weighs 222 N on Mars? l