Name Block
I. Newton’s First Law
A. Force—push or pull on an object
The combination of all the forces acting on an object is the net force.1.
2. When forces are balanced forces, they cancel each other out and do not change an object’s motion; when forces are unbalanced forces, the motion of an object changes.
B. Newton’s first law of motion—an object will remain at rest or move with constant speed unless a force is applied.
C. Friction is a force that resists sliding between two touching surfaces or through air or water.
Friction slows down an object’s motion.1.
2. Static friction—the type of friction that prevents an object from moving when a force is applied.
3. Sliding friction is due to the microscopic roughness of two surfaces; it slows down a sliding object.
4. Rolling friction between the ground and a wheel allows the wheel to roll.
II. Newton’s Second Law
A. Newton’s second law of motion connects force, acceleration, and mass; it explains that an object acted upon by a force will accelerate in the direction of the force; acceleration equals net force divided by mass.
B. Gravity—attractive force between two objects; depends on the mass of the objects and distance between them; gravitational force is also called weight.
C. The second law explains how to calculate the acceleration of an object if its mass and the forces acting on it are both known.
D. In circular motion, the centripetal force is always perpendicular to the motion.
E. The terminal velocity is reached when the force of gravity is balanced by air resistance; the size of the air resistance force depends on the shape of an object and its speed.
F. An object can speed up, slow down, or turn in the direction of the net force when unbalanced forces act on it.
III. Newton’s Third Law
A. Newton’s third law of motion
states that forces always act in equal but opposite pairs; for every action there is an equal and opposite reaction.B. Action-reaction forces are always the same size but are in opposite directions and act on different objects.
When the mass of one object is considerably larger than the mass of another object, the action-reaction force is not noticeable.1.
2. Air and water exert action-reaction forces with objects such as hands or canoe paddles.
3. A rocket launches due to the equal but opposite forces of the burning fuel.
IV. Pressure
A. Pressure—force per unit area that is applied on the surface of an object
B. Pressure can be calculated with a formula: pressure (Pa) = force (N) / area (m2) or P = F/A.
The SI unit of measure for pressure is the pascal. (Pa).1.
One pascal is equal to a force of 1 N applied over an area of 1 m2, or 1 Pa = 1 N/m2.a.
b. The area is the area of contact in which the pressure is exerted.
c. Pressure increases if the force applied increases or the area decreases.
d. The weight of a dollar bill resting flat on a table exerts a pressure of about 1 Pa on the table.
2. 1 Pa is such a small unit of measure that pressure is sometimes expressed in units of kPa, or 1,000 Pa.
3. Sometimes, the force that is exerted is the weight of an object.
4. Changing the area over which force is applied is one way to change the pressure that is exerted on an object.
V. Doing Work with Fluids
Fluids at rest and in motion can exert forces that do useful work.A.
1. Pushing on a fluid can increase pressure.
2. The pressure the fluid exerts is increased by the amount of the additional force being applied.
B. Pascal’s principle—when a force is applied to a fluid in a closed container, the pressure throughout the fluid increases by the same amount.
C. A hydraulic system uses a fluid to increase an applied force.
D. Bernoulli’s principle—when the speed of a fluid increases, the pressure exerted by the fluid decreases.
A fluid will move from a higher pressure environment to a lower pressure environment.1.
2.Wind can increase the rate at which smoke rises in a chimney.
3. Hurricanes and other high winds can decrease the air pressure outside a house and the roof can be pushed off the house by the higher pressure of the still air inside.
E. Moving air produces a force that allows planes and birds to fly.
Lift is created by downward flowing air which exerts an upward reaction force on the wing.1.
2. Increasing the size or surface area of the wing can increase lift.
3. Planes and birds have various wing shapes depending on the type of flight.
Seabirds and gliders have long, narrow wings that help them glide long distances.a.
b. Swallows, swifts, falcons, and jet fighter airplanes have small, narrow, tapered wings to help them fly at high speeds.
c. Forest and field birds, such as pheasants, have short, rounded wings that allow for quick take-offs and sharp turns.