Enduring Understanding: Studying dynamics (causes of motion) has had a profound effect on the way humans view their world. Essential Question: What may be accomplished by understanding dynamics? Essential Question: How may we symbolically represent dynamics information? Essential Question: How are dynamics a predictor of kinematics?

Isaac Newton

Joe Perry from Aerosmith?

Newton’s Laws -Built on Galileo’s ideas -If I have seen farther it is by standing on the shoulders of Giants

Today, we agree with Newton’s Laws of Motion. These laws of motion differ from the views of Aristotle and the Ancient Greeks.

Aristotle on Motion -Natural Motion : Vertical Motion. Falling objects or smoke rising. No force recognized.

Violent Motion Was motion with a visible force. It was also believed that an objects natural position was at rest.

The Rolling Ball Demo Open the document

Forces cause objects to accelerate. A New View of Motion Force (F) – a push or pull - measured in Newtons (N) - vector quantity, direction matters

Newton’s First Law: Law of Inertia Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by unbalanced forces exerted upon it.

Real Newton’s 1 st Law Failures On 2 nd thought, I think he did this on purpose!

Inertia Resistance to change More mass means more inertia because it requires a greater force to change its speed or direction.

Answer the Questions on the Newton’s 1 st Law document

Contact Forces Action-at-a-Distance Forces (Field Forces)

Examples of Forces Applied Force (F a ) - An applied force is a push or pull acting on an object by another object or person. Normal Force (F N or N) - the support force exerted upon an object that is on a surface.  Directed perpendicularly to the surface the object is on.

Frictional Force (F f ) - force exerted by a surface as an object moves across it or makes an effort to move across it. - opposite direction of motion - Rough surface  more friction - The result of molecules from each object creating instantaneous bonds with each other.

Mass vs Weight Mass (m) the amount of matter or inertia. SI unit is kilograms (kg) Is the same at every location. Gravitational Force (W or F g ) - the force with which the earth, moon, or other massive body attracts an object towards itself. This is the weight of an object. Varies depending upon location, mass, acceleration due to gravity.

To calculate weight: W = m x g W is weight, m is mass in (kg), g the acceleration due to gravity is 9.8 (m/s 2 ) at sea level on earth.

Calculations Involving Weight Unless told otherwise, assume the problems take place at sea level on earth. What is the weight of a 1 kg object? W = mg W = 1(kg) x 9.8(m/s 2 ) = 9.8(N) The Newton (N) is derived from the units (kg), (m)eter and (s)econd.

What is the weight of a 2 kg object? 19.6 N What is the mass of a 250 N object? 25.5 kg

Try 1-8 Newton’s First Law Practice

The Normal Force is also known as the support force. Weight, the force due to gravity always acts on an object.

the weight and the normal force are equal in size and opposite in direction.

Try # 9 & 10

How does it work?

Net Force At least one force is acting on every object at all times. Net Force is the total of all the forces.

All Forces are measured in Newtons. In the tug of war, if the team on the left pulls with a force of 1200 N and the team on the right pulls with 1000 N, what is the net force?

Answer 200 N to the left

Try Problems 11-20

Forces Can Be Added As Vectors. A free body diagram is used to identify the forces acting on an object.

More Free Body Diagrams

Equilibrium At Equilibrium all forces are balanced. The net force is zero. A number of large forces act on a bridge. What are they?

What happens if the forces acting on a bridge are not in equilibrium?

Can an object be at equilibrium and still be moving?

Yes According to The Law of Inertia, an object in motion will stay in motion at the same speed if all of the forces are in balance.

If the forces become out of balance, the object will slow down, speed up or change direction.

Free Body Diagram Practice A box is at rest on a table. Draw a free body diagram of the forces acting on it. _____________________________________________________________

weight normal force

The normal force and the weight always act on an object on a surface.

_________________________________________________________ A person pushes a box to the right. Draw a free body diagram of the forces acting on it.

____________________________________________________________ F g or W F N or N FaFa FfFf