Forces Notes
A force is defined as a push or a pull. Forces are acting all around you all of the time. Forces occur in pairs. For instance, just in the act of standing there are 2 primary forces acting. Your body pushing down on the floor/ground and the floor/ground pushing back up on you. To open a door you have to pull on the door and the door pulls back against your hand. Forces are measured in units called newtons.
Balanced vs unbalanced forces- Forces may be balanced or unbalanced. The conditions for balanced forces are [1] the object is not moving [2] the object moves at a constant speed. Examples: 1] a book lying on a table has balanced forces 2] the motion of the Earth around the Sun would be constant motion. Unbalanced forces , generally speaking, involve an object in motion. As most moving objects on Earth do not move at a constant speed, they are considered to have unbalanced forces acting on them. Ex: you walking, you blinking.
Friction
Friction is a force that opposes motion (keeps things from moving freely). There are 3 types of friction: rolling ( ball moving on ground, wheels on a moving skateboard....), sliding (going down a playground slide, holding any object- holding a cell phone, sunglasses on your head...) and fluid (any object moving through water or air is said to have fluid friction...fish swimming, ball thrown through air....AND snow skiing, ice skating, snowboarding... the reason these are is that a thin layer of water forms underneath them & that makes it fluid friction)
Newton's Laws of Motion
Newton's First Law of motion states that an object at rest will stay at rest and an object in motion will keep moving UNLESS an unbalanced force acts on it to change that. Newton's First Law is called the law of inertia. Inertia is the tendency of objects to resist any change in what they are doing. A book lying on a desk demonstrates the 1st law because it is not moving and would stay there unless someone or something exerted a force on it to move. Also, when you throw a ball the ball has a tendency to keep moving in a straight line AND at a constant speed continually without changing. However, the gravity of Earth and the friction of the air slow it down and eventually stop it.
Newton's Second Law of motion states that the acceleration of an object depends on the force applied to the object and its mass. The equation is Force = mass x acceleration. Another way of looking at is like this- if I was to give you a golf ball and a bowling ball (different masses) and ask you to accelerate each at the same rate, say 10 m/s/s, it would require more force to accelerate the bowling ball due to its greater mass than the golf ball.
Newton's Third Law of motion states that for every action force there is an equal and opposite reaction force. Remember- forces always occur in pairs. Example: if you are sitting in a chair your body is pushing down on the chair with as much force as the chair is pushing back up on your body. If you lean against your locker, the locker pushes back with as much force as you push on it (equal & opposite).
Mass vs. Weight
Mass is the amount of matter in an object and differs from weight because weight is the affect of gravity on the mass of an object. QUESTION: Where would you have the most weight, on Earth or on the Moon? answer: the Earth because the Earth has a greater gravitational force on you than the moon.
Another QUESTION: Where would you have mass but no weight? answer: outer space
Gravity is a force of attraction between two objects and depends upon the objects masses and the distances between the objects.
The more massive the objects the more gravity pulls and vice versa. The more the distance between objects the lesser the gravity and vice versa.
Gravitational acceleration on Earth is 9.8 m/s/s. That means that for every second an object falls its speed increases by 9.8 m/s.
Problem: After 3 seconds of freefall, how fast would a ball be traveling? after 4 seconds of freefall? after 5 seconds?
answers: 9.8 m/s/s x 3s = 29.4 m/s 9.8 m/s/s x 4 sec=? 9.8 m/s/s/ x 5 sec= ?
Balanced vs unbalanced forces- Forces may be balanced or unbalanced. The conditions for balanced forces are [1] the object is not moving [2] the object moves at a constant speed. Examples: 1] a book lying on a table has balanced forces 2] the motion of the Earth around the Sun would be constant motion. Unbalanced forces , generally speaking, involve an object in motion. As most moving objects on Earth do not move at a constant speed, they are considered to have unbalanced forces acting on them. Ex: you walking, you blinking.
Friction
Friction is a force that opposes motion (keeps things from moving freely). There are 3 types of friction: rolling ( ball moving on ground, wheels on a moving skateboard....), sliding (going down a playground slide, holding any object- holding a cell phone, sunglasses on your head...) and fluid (any object moving through water or air is said to have fluid friction...fish swimming, ball thrown through air....AND snow skiing, ice skating, snowboarding... the reason these are is that a thin layer of water forms underneath them & that makes it fluid friction)
Newton's Laws of Motion
Newton's First Law of motion states that an object at rest will stay at rest and an object in motion will keep moving UNLESS an unbalanced force acts on it to change that. Newton's First Law is called the law of inertia. Inertia is the tendency of objects to resist any change in what they are doing. A book lying on a desk demonstrates the 1st law because it is not moving and would stay there unless someone or something exerted a force on it to move. Also, when you throw a ball the ball has a tendency to keep moving in a straight line AND at a constant speed continually without changing. However, the gravity of Earth and the friction of the air slow it down and eventually stop it.
Newton's Second Law of motion states that the acceleration of an object depends on the force applied to the object and its mass. The equation is Force = mass x acceleration. Another way of looking at is like this- if I was to give you a golf ball and a bowling ball (different masses) and ask you to accelerate each at the same rate, say 10 m/s/s, it would require more force to accelerate the bowling ball due to its greater mass than the golf ball.
Newton's Third Law of motion states that for every action force there is an equal and opposite reaction force. Remember- forces always occur in pairs. Example: if you are sitting in a chair your body is pushing down on the chair with as much force as the chair is pushing back up on your body. If you lean against your locker, the locker pushes back with as much force as you push on it (equal & opposite).
Mass vs. Weight
Mass is the amount of matter in an object and differs from weight because weight is the affect of gravity on the mass of an object. QUESTION: Where would you have the most weight, on Earth or on the Moon? answer: the Earth because the Earth has a greater gravitational force on you than the moon.
Another QUESTION: Where would you have mass but no weight? answer: outer space
Gravity is a force of attraction between two objects and depends upon the objects masses and the distances between the objects.
The more massive the objects the more gravity pulls and vice versa. The more the distance between objects the lesser the gravity and vice versa.
Gravitational acceleration on Earth is 9.8 m/s/s. That means that for every second an object falls its speed increases by 9.8 m/s.
Problem: After 3 seconds of freefall, how fast would a ball be traveling? after 4 seconds of freefall? after 5 seconds?
answers: 9.8 m/s/s x 3s = 29.4 m/s 9.8 m/s/s x 4 sec=? 9.8 m/s/s/ x 5 sec= ?