# Forces and Newton’s Laws

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Forces and Newton’s Laws

Force A Force is a push or a pull that one body exerts on another.
All Forces are measured in Newtons (N)

Balanced Forces Force that are equal in opposite directions and act on an object to produce a net force of zero. 20N Net force = 0 20N Balanced Forces cause no change in motion

Unbalanced Forces Forces acting on an object to produce a net force that is positive. 20N Net force = 5N Box moves to the right 15N Unbalanced Forces cause a change in motion.

Some Types of Forces Friction is the force between two objects that opposes the motions of either object. Example: Rubbing your hands together.

Some Types of Forces Air Resistance is the force that acts on objects as they move through air. The amount of air resistance acting on an object depends on two factors: 1) Speed (Velocity). The faster an object moves, the more air resistance acts on it More air resistance Less air resistance 2) Surface area. The larger the surface area of an object the more air resistance acts in it. Crumpled paper Flat paper Less air resistance More air resistance

Some Types of Forces Gravity is the force that holds everything in the universe together. “Every object in the universe exerts the force of gravity on all other objects.” Gravity depends on two factors: 1) Distance. The shorter the distance between two objects the greater the force of gravity between them More Gravity Less Gravity 2) Mass. The greater the mass of an object, the more gravity it exerts on other objects. More Gravity Less Gravity

Some Types of Forces Weight is a force. It is the force that gravity exerts on an object due to the object’s mass. “Like all forces weight is measured in Newtons.” Weight depends on two factors: Weight = MassxGravity 1) Mass. The more mass an object has, the more gravity acts on it and the more weight it has. 10kg 5kg More Weight 5N Less Weight 2.5 N

weight = mass x acceleration of gravity
Some Types of Forces weight = mass x acceleration of gravity W = mg W m g

Some Types of Forces Jupiter Earth Less Weight 2.5 N More Weight 5N
2) The amount of Gravity on the planetary body the object is on. Jupiter Earth 10kg 10kg Less Weight 2.5 N More Weight 5N

Sir Isaac Newton

Newton’s First Law It is often called the Law of Inertia.
Newton’s First Law states, “An object at rest will remain at rest unless acted upon by an unbalanced force while an object in motion will remain in motion with constant speed and direction unless acted upon by an unbalanced force” It is often called the Law of Inertia.

What is inertia? An object’s tendency to resist a change in it’s motion. This means that an object: Will be hard to move if it is at rest Example: The plates on a set table. Or a tomato being shot.

NO…why? Would the bowling ball and the golf ball have the same
inertia? NO…why? The more massive an object is, the greater its inertia… And the greater an objects inertia is, the greater the force required to put the object in motion

Examples of Inertia Will be hard to slow an object down or speed it up if it is moving Example People involved in a car stopping suddenly fly forwards because they keep moving at the same speed as the car. Only the seatbelt stops them.

Newton’s Second Law of Motion
Newton’s Second Law states, “When a net force acts on an object the object will accelerate in the direction of the net force”. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object). Everyone knows that heavier objects require more force to move the same distance as lighter objects

Newton’s Second Law of Motion
Newton’s Second Law gives us an exact relationship between force, mass, and acceleration. It Sates that the amount of force needed to move an object is equal to it’s mass multiplied by its acceleration FORCE = MASS times ACCELERATION

Example of how Newton's Second Law works
Mike's car, which weighs 1,000 kg, is out of gas. Mike is trying to push the car to a gas station, and he makes the car go 0.05 m/s/s. How much force is Mike using? F M A Answer = 50 newtons

Newton’s Third Law of Motion
Newton’s Third Law states, “For every action there is an equal and opposite re-action” What does this mean? This means that for every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard.

Newton’s Third Law of Motion
Explains how a rocket works The rocket's action is to push down on the ground with the force of its powerful engines, and the reaction is that the ground pushes the rocket upwards with an equal force.

Quiz 1) Who was the scientist who gave us the Laws of Motion?
2 What is another name for the first law of motion? 3) Which law explains why we need to wear seatbelts? 4) Which law says that force is equal to mass times acceleration (F=MA)?