Sir Isaac Newton (1643-1727) an English scientist and mathematician famous for his discovery of the law of gravity also discovered the three laws of motion .
Today these laws are known as Newton’s Laws of Motion and describe the motion of all objects on the scale we experience in our everyday lives.
Remember: Technology is limited by laws of nature such as these!!!
Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.
A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.
The normal force is the support force exerted upon an object which is in contact with another stable object.
For example, if a physics book is resting upon a table, then the table is exerting an upward force upon the book in order to support the weight of the book.
Non contact forces are those types of forces which result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation.
Non-Contact forces generate a force field – the area influenced by the push or pull of the non contact force.
ALL objects attract each other with a force of gravitational attraction.
The standard formula for gravity is:
Gravitational force = (G * m1 * m2) / (d2)
where G is the gravitational constant, m1 and m2 are the masses of the two objects for which you are calculating the force, and d is the distance between the centers of gravity of the two masses.
Electric and magnetic forces are non contact forces.
The protons in the nucleus of an atom and the electrons outside the nucleus experience an electrical pull towards each other despite their small spatial separation.
Two magnets can exert a magnetic pull on each other even when separated by a distance of a few centimeters.
Electric and magnetic forces are stronger than gravity but only work over very small distances
This trick works because the inertia of the heavy objects tends to keep them in place.
By quickly pulling the tablecloth, the force of friction is easily overcome.
If the tablecloth was pulled slowly, the friction would be greater than the inertia, and the dishes would follow along.
(Note: The tablecloth must be pulled down at the edge, otherwise the dishes may fly upward.)
24.
If objects in motion tend to stay in motion, why don’t moving objects keep moving forever? Things don’t keep moving forever because there’s almost always an unbalanced force acting upon it. A book sliding across a table slows down and stops because of the force of friction . If you throw a ball upwards it will eventually slow down and fall because of the force of gravity . In outer space, away from gravity and any sources of friction, a rocket ship launched with a certain speed and direction would keep going in that same direction and at that same speed forever .
Blood rushes from your head to your feet while quickly stopping when riding on a descending elevator.
The head of a hammer can be tightened onto the wooden handle by banging the bottom of the handle against a hard surface.
To dislodge ketchup from the bottom of a ketchup bottle, it is often turned upside down and thrusted downward at high speeds and then abruptly halted.
Headrests are placed in cars to prevent whiplash injuries during rear-end collisions.
While riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb or rock or other object which abruptly halts the motion of the skateboard.
The weight of an object changes with location, the mass of an object does not.
For example, your mass is the same on earth and on the moon but you weigh less on the moon because, due to its smaller size, the moon has a weaker pull of gravity.
Imagine a ball of a certain mass moving at a certain acceleration. This ball has a certain force (double the mass) but keep the acceleration constant. F = ma says that this new ball has twice the force of the old ball.
Now imagine the original ball moving at twice the original acceleration. F = ma says that the ball will again have twice the force of the ball at the original acceleration.
Now imagine we make the ball twice as big
35.
Examples of the Second Law F = ma basically means that the force of an object comes from its mass and its acceleration. Something very small (low mass) that’s changing speed very quickly (high acceleration), like a bullet, can still have a great force. Something very small changing speed very slowly will have a very weak force. Something very massive (high mass) that’s changing speed very slowly (low acceleration), like a glacier, can still have great force.
Whenever two objects interact, the force exerted on one object is equal in size and opposite in direction to the force exerted on the other object.
F A due to B = F B due to A
In other words…….For every force acting on an object, there is an equal force acting in the opposite direction.
38.
What does this mean? Right now, gravity is pulling you down in your seat, but Newton’s Third Law says your seat is pushing up against you with equal force . This is why you are not moving. There is a balanced force acting on you– gravity pulling down, your seat pushing up.
39.
Think about it . . . What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force. Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts).
A bird flies by use of its wings. The wings of a bird push air downwards. Since forces result from mutual interactions, the air must also be pushing the bird upwards.
The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards).
For every action, there is an equal (in size) and opposite (in direction) reaction. Action-reaction force pairs make it possible for birds to fly.