This unit our class learned about Newton's first and third law, force vectors, free body diagrams, and mass and weight. We practiced creating FBDs that depicted an object at rest, accelerating, and in motion. A force is an interaction between 2 objects, either pushed or pulled.
Newton's First Law
Newton's First Law of Motion states that "an object at rest and an object in motion will remain in motion with the same speed and and in the same direction unless acted upon by an unbalanced force." An example of this law is when Ms. Lawrence threw a ball straight up in the air and it came back down, with no forces acting on it.
Newton's Third Law
Newton's Third Law of Motion states that "for every action, there is an equal and opposite reaction." For every interaction between two objects there is a pair of forces acting on both. The size of the force acting on the first object is equivalent to the size of the force acting on the second object. When you press your shoe into the grass, there is a force that the sole of your shoe is pushing onto the ground and a force coming back from the grass, to your shoe. (Every action has an equal & opposite reaction.)
Free body diagrams were used throughout this unit to help illustrate forces acted upon an object. We only include forces acting upon the object and not forces that the object is creating.
Normal Force
The normal force acts in the opposite direction of gravity. It is the support force exerted upon an object that is touching another stable object. It is represented with Fn. This vector always goes perpendicular to the surface the object is resting upon.
Gravitational Force
A gravitational force is the pull of gravity towards the center of the earth, therefor the vector always points downward. It is a force that attracts any object with mass and is represented with Fg.
Frictional Force
A frictional force is opposite the direction the object is moving. This force is exerted by a surface as an object moves across it or tries to. It is always parallel to the surface the object is on and is represented with Ff.Tension Force
This is a force that is transmitted through a rope or wire and is represented by Ft. The tension runs along the direction the rope is pulled.
Tilting an Axis
When an object is being pulled or resting on a surface that is at an angle, we can rotate our free body diagrams. The x-axis is tilted to the angle of the surface.
Vectors
Vectors are the arrows we use in free body diagrams. In the example above, both Fnorm and Fgrav have arrows in equal length. This signifies that the forces are equal, but if Fgrav was longer that would mean it has a larger force than the smaller one (Fnorm).
Balanced Diagrams
In the example above, the free body diagram is balanced despite the fact that the object is in motion. There is a normal force pushing up, a gravitational force pulling it down towards the earth, a frictional force going against the direction the object is moving, and a push force directing the object to the right. We can conclude that the object is moving at a constant velocity since it is balanced. As shown at the bottom of the picture, F(net)=0N.
Unbalanced Diagrams
As discussed in class, tug of war is a great example of balanced and unbalanced forces. If the two teams are exerting an equal amount of force, 300 N vs. 300 N, then neither team would win. However, in the picture above, the team to the left is exerting more force into the ground and thus has 100 more newtons of force than the team on the right. Whoever has more friction between the ground and their shoes wins the game.
Part B
This unit was more applicable to everyday life in comparison to the last unit, as the class used more real world examples to demonstrate our knowledge. Initially we used the hovercraft, then simply throwing the ball in the air, tug of war, horse pulling a cart, and wearing a seatbelt. Forces are used all the time, everyday. When we place objects down on the table or participate in a game of tug of war, forces are acting unknowingly to us. Newton's Laws also helped prove some counterintuitive thinking wrong.
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