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# Forces

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## Leanne Hilkowski

on 20 October 2013

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#### Transcript of Forces

Forces

Define a force
A force is a push or a pull that acts on an object.
A force can cause a resting object to move, or it can accelerate a moving object by changing the object's speed or direction.

Action-Reaction
The first force is the action force
The second force is the reaction force
Momentum
The product of an object's mass and it's velocity.
Universal Forces
All universal forces act over a distance between particles of matter, which means that the particles need not be in contact in order to affect one another.
Types of Forces
Forces can be balanced or unbalaced. They can be adding forces, subtracting forces, or equal and opposite forces.
Newton's Laws of Motion
It took about 2000 years for scientists to develop an understanding between force and motion. Aristotle and Galileo both had a go at the tast before Newton published his findings.
Gravitational Force
Gravitational force is an attractive force that acts between any two masses.

Newton's law of universal gravitation states that every object in the universe attracts every other object.
Conclusion
Newtons
Force is measured in newtons, N.
One newton is the force that causes a 1-kilogram mass to accelerate at a rate of

1 meter per second each second
1 m/s
1 newton is equal to 1 kg * m/s
Representing Force
Arrows are used to represent the strength and direction of a force.
Combining Forces
Net force is the overall force acting on an object after all the forces are combined.
Friction
Friction is a force that opposes the motion of objects that touch as they move past each other.
There are four main types of friction:
Static Friction
Sliding Friction
Rolling Friction
Fluid Friction
Gravity
Gravity is a force that acts between any two masses.
Projectile Motion
The motion of a falling object after it is given an initial forward velocity.

The combination of an initial forward velocity and the downward vertical force of gravity causes the ball to follow a curved path.
First Law
The state of motion of an object does not change as long as the net force acting on the object is zero.
Second Law
The acceleration of an object is equal to the net force acting on it divided by the object's mass.
Third Law
Whenever one object exerts a force on the second object, the second object exerts an equal and opposite force on the first object.
Determining
Imagine a swimmer using her arms to push against the water. The swimmer is pushed forward in the water.

Which is the action force?
Which is the reaction force?
Do Not Cancel
Why don't action and reaction forces create a net force of zero?
Formula
The formula for momentum is:

Momentum = Mass x Velocity

Velocity is measured in m/s
Momentum is measured in kg x m/s
Conservation
Law of conservation of momentum states that if no net force acts on a system, then the total momentum of a system does not change.

In a closed system, the loss of momentum of one object equals the gain in momentum of another object.
Electromagnetic Forces
These forces are associated with charged particles. Electric force and magnetic force are the only forces that can both attract and repel.
Electric forces
Magnetic forces
Nuclear Forces
Two forces: Strong nuclear force and Weak nuclear force, act within the nucleus to hold it together.
Distance
Gravitational force is proportional to their masses and decreases rapildy as the distance between the masses increases.
Earth, Moon, Tides
Centripetal force is a center-directed force that continuously changes the direction of an object to make it move in a circle.

The gravitational pull from the moon produces two bulges in Earth's oceans. One is on the side of Earth closest to the moon. The other is on the farthest side.
Refer back to the pros and cons
Explain how it will help
Describe the next steps
Based on Jim Harvey's speech structures
2
2
Which has greater force?
Math practice: Page 367, 1-4
Weight vs. Mass
Weight and mass are not the same thing.
Weight: the force of gravity acting on an object.

Weight = Mass x Acceleration due to gravity
http://www.wisc-online.com/Objects/ViewObject.aspx?ID=TP1402
The action and reaction forces do not act on the same object.
An object has a large momentum if the product of its mass and velocity is large.
Strong force: a powerful force of attraction that acts only on the neutrons and protons in the nucleus, holding them together. The range it acts over is apprx. equal to the diameter of a proton, but it is 100 times stronger than the electric force of repulsion.
Weak force: an attractive force that acts only over a short range. It is involved in nuclear decay.
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