FORCE Chapter 10 Text

Force A push or a pull in a certain direction SI Unit = Newton (N)

Combining Forces The combination of all forces acting on an object is the Net Force.

When forces act in the SAME DIRECTION = ADDITION

When forces act in the OPPOSITE DIRECTION = SUBTRACTION

Balanced Forces result in NO MOVEMENT

= 0

Unbalanced forces cause a change in the object’s motion.

=

=

Friction and Gravity Friction – the force that two surfaces exert on each other when they rub

Types of Friction 1. Static Friction 2. Sliding Friction 3. Rolling Friction 4. Fluid Friction

Static Friction Friction that acts on objects that are NOT moving

Sliding Friction Occurs when two surfaces slide over each other

Rolling Friction Occurs when an object rolls across a surface

Fluid Friction Occurs when solid objects moves through fluids such as water, oil, or air

Friction depends on two factors: 1. How hard the surfaces push together

2. The type of surfaces involved

Gravity A force that pulls objects toward each other

2 Factors Affecting Gravity 1. Distance 2. Mass

If Distance Increases the force of gravity Decreases

Mass The amount of matter in an object

If mass increases, the force of gravity increases

Mass vs. Weight Mass is Constant because of the amount of matter does not change

The force of gravity on a person or object at the surface of a planet is known as weight.

Weight varies with the strength of the gravitational force, mass does not.

Gravity and Motion Free fall – when the only force acting on a falling object is gravity

Acceleration due to gravity is 9.8 m/s/s

All objects in free fall accelerate at the SAME rate regardless of their masses

Why don’t objects fall at the same rate?

Air Resistance Falling objects with a greater surface area experience more air resistance.

Terminal Velocity Reached when the force of air resistance equals the weight of the object

Newton’s Laws of Motion

Newton’s 1 st Law an object at rest will remain at rest, an object in motion will stay in motion UNLESS acted upon by another force.

Inertia Resistance to a change in motion Newton’s 1 st Law

Inertia depends on mass, the greater the mass the greater the inertia

Newton’s 2 nd Law Force = mass x acc.

Acceleration =Net Force Mass

End Unit for Acceleration kgm/s/s Kgm/s 2 Newton

Textbook samples

Calculating: Calculate the slope of the graph. What does the slope tell you about the object’s motion?

The slope is 9.8. The speed increases by 9.8 m/s each second.

– What will the speed of the object be at 6 seconds? 58.8 m/s

A speedboat pulls a 55- kg water-skier. The force causes the skier to accelerate at 2.0 m/s 2. Calculate the force that causes this acceleration.

F net = m X a = 55 kg X 2.0 m/s 2 F = 110 kg m/s 2 F = 110 N

What is the net force on a 1,000-kg object accelerating at 3 m/s 2 ?

Force = m x acc. (1,000 kg X 3 m/s 2 ) 3,000 N

What net force is needed to accelerate a 25-kg cart at 14 m/s 2 ?

Force = mass x acc. (25 kg X 14 m/s 2 ) 350 N

Newton’s 3 rd Law For every action there is an equal and opposite reaction

Momentum Momentum = Mass x Velocity End Unit = kg m/s

Conservation of Momentum The total momentum of any group of objects remains the same, or is conserved, unless outside forces act on the objects

Which has more momentum: a 3.0-kg sledgehammer swung at 1.5 m/s or a 4.0-kg sledgehammer swung at 0.9 m/s?

Momentum = Mass X Velocity Smaller sledgehammer = 3.0 km X 1.5 m/s = 4.5 kgm/s Larger sledgehammer = 4.0 km X 0.9 m/s = 3.6 kgm/s

A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is kg and the mass of the baseball is 0.14 kg. Which has the greater momentum?

Golf ball: kg X 16 m/s = 0.72 kgm/s Baseball: 0.14 kg X 7 m/s = 0.98 kgm/s The baseball has greater momentum.

What is the momentum of a bird with a mass of kg flying at 15 m/s?

(0.018 kg X 15 m/s = 0.27 kgm/s

Energy Chapter 13

Energy The ability to do work

2 Kinds of Energy 1. Kinetic Energy 2. Potential Energy

Kinetic Energy Energy of MOTION

Kinetic energy increases as mass and velocity increases

Potential Energy Stored Energy

Gravitational potential energy increases as weight and height increase.