Force and Newton’s 3 Laws of Motion

Reginald Cruz| Illiana Aguirre| Physics 270

What is Force and Newton’s 3 Laws of Motion? Today, we’re going to explain what Force is, Newton’s 3 Laws, and Gravity with Weight

Force and Newton’s 3 Laws of Motion

• Force is anything that pulls or pushes an object. The amount of force to the object will change the motion of the object or prevent the object from chaning motion.

• Example: DragonBall Z throws a fireball at Chung-Li (Streetfighter) during a battle. The amount of force Z uses to throw the fireball can change the motion of where the fireball will hit, in this case, it will knock Chung-Li down to the ground on impact.

Newton’s Three Laws of Motion

• Law of Inertia-Page 126: “A Body that is in motion continues in motion with the same velocity (at constant speed and in a straight line) and a body at rest continues to rest unless an unbalanced outside) force acts upon it”.

• Law of Acceleration-Page 128: “The total force acting on a body is equal to the mass of the body times its acceleration”.

• Law of Action and Reaction-Page 140: “For every force applied by object A to object B (action), there is an equal but opposite force exerted by object B to object A (reaction)”.

Law of Inertia

Example

• A car moving on the road in motion will continue to move until it stops.

2nd example

• When riding a bus (like Muni or BART), also applies to Newton’s first law. The bus stops at a point in time, then it will stay at rest until it moves on.

Third example

• Walking from one point to another follows Newton’s first law.

• If you stop at a midpoint and rest, then you will stay at rest then use more velocity unless an unbalanced force acts upon it.

Law of Acceleration (Newton’s 2nd Law)It states the total force acting on a body is

equal to the mass of the body times its acceleration.

The equation is F = ma where F is the total force, m = mass, and a = acceleration

Here’s how we would use it: Back to the first scenario on the battle between Dragonball Z and Chung-Li. What force is necessary for Chung-Li to throw a fireball back at Dragaonball Z if the mass (m) of the fireball is 1500 kg and the acceleration of the fireball is 100 m/s2.

Solution

• First, we know m = 1500 kg and a = 100 m/s2 and F = ?

• The equation is F = (1500 kg)(100 m/s2)

• The amount of force is 150,000 kg m/s2 or 150,000 N (1 N = 1 kg m/s2) needed for her shot to hit Dragonball Z.

Another example of Newton’s 2nd Law

• What is the acceleration of a ball being kicked by a force of 950 N applied to the mass of 900 kg?

• The Force = 950 N and Mass = 900 kg and a = ?

• To find the acceleration, F = ma a = F/m

• Then a = (950 N)/(900 kg)

• which a = (950 N)/(900 kg) * 1 kg m/s2/1 N

• The acceleration of the ball is 1.05 m/s2.

Gravity and Weight

• The weight of an object is based on the amount of the gravitational pull exerted on an object by the earth.

• An example is if a satellite dish falls from space as it enters the earth’s atmosphere. The weight of the dish is being pulled by the gravity from earth.

• It also gives this equation (Section 5.3 Page 131): Fw = mg where Fw = the weight, m = mass, g = acceleration due to gravity, g = 9.80 m/s2 or g = 32.2 ft/s2.

Problem Scenario involving Gravity and Weight

• What is the weight of a rock with a mass of 350 kg?

• Solution: m = 350 kg g = 9.80 m/s2 Fw = ?

• Fw = (350 kg)(9.80 m/s2) 3430 kg m/s2 or 3430 N (1 N = 1 kg m/s2)

Works Cited

Ewen, Dale, Neill Schurter and Erik P Gundersen. Applied Physics . 10th Edition. Upper Saddle River: Peasrson Education Inc, 2012. textbook. 7 April 2015.