forces. - the nature of force combining forces the combination of all forces acting on an object is...
TRANSCRIPT
Forces
Forces - The Nature of Force
Combining Forces
The combination of all forces acting on an object is called the net force.
Forces - The Nature of Force
Unbalanced Forces
Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion.
Forces - The Nature of Force
Balanced Forces
Balanced forces acting on an object do not change the object’s motion.
Forces
Asking QuestionsBefore you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions.
What is a force? A force is a push or pull.
What happens when forces combine?
Forces combine to produce a net force.
Question Answer
- The Nature of Force
Forces - Friction and Gravity
Gravity
Two factors affect the gravitational attraction between objects: mass and distance.
Forces - Friction and Gravity
Gravity
The force of gravity on a person or object at the surface of a planet is known as weight.
Forces - Friction and Gravity
Forces
Free Fall
Use the graph to answer the following questions.
- Friction and Gravity
Forces
Free Fall
Time is on the horizontal axis, and speed is on the vertical axis.
Interpreting Graphs:
What variable is on the horizontal axis? The vertical axis?
- Friction and Gravity
Forces
Free Fall
The slope is 9.8. The speed increases by 9.8 m/s each second.
Calculating:
Calculate the slope of the graph. What does the slope tell you about the object’s motion?
- Friction and Gravity
Forces - Friction and Gravity
Air Resistance
Falling objects with a greater surface area experience more air resistance.
Forces
Friction Gravity
Comparing and ContrastingAs you read, compare and contrast friction and gravity by completing a table like the one below.
Effect on motion Opposes motionPulls objects toward one another
Depends onTypes of surfaces involved, how hard the surfaces push together
Mass and distance
Measured in Newtons Newtons
- Friction and Gravity
Forces
Calculating Force
A speedboat pulls a 55-kg water-skier. The force causes the skier to accelerate at 2.0 m/s2. Calculate the net force that causes this acceleration.
Read and Understand
What information have you been given?
Mass of the water-skier (m) = 55 kg
Acceleration of the water-skier (a) = 2.0 m/s2
F = ma
F = 55 kg x 2 m/s2 = 110 N
- Newton’s First and Second Laws
Forces
Calculating Force
Practice Problem
What is the net force on a 1,000-kg object accelerating at 3 m/s2?
3,000 N (1,000 kg X 3 m/s2)
- Newton’s First and Second Laws
Forces
Newton’s First LawIf no forces are exerted on an object, the object
continues in its original state of motionNewton’s Second LawThe acceleration of an object is proportional to the
force acting on it and inversely proportional to the mass of the object
F = ma What if a=0 ?
Newton’s Third LawIf two objects interact they exert equal forces on
each other in opposite directions
Forces
Newton’s First and Second Laws
I. Newton’s First Law of MotionA. InertiaB. Inertia Depends on Mass
II. The Second Law of MotionA. Changes in Force and Mass
- Newton’s First and Second Laws
Forces
Calculating Momentum
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?
Read and Understand
What information have you been given?
Mass of smaller sledgehammer = 3.0 kg
Velocity of smaller sledgehammer = 1.5 m/s
Mass of larger sledgehammer = 4.0 kg
Velocity of larger sledgehammer = 0.9 m/s
- Newton’s Third Law
Forces
Calculating Momentum
Momentum = Mass X Velocity
Perform the calculation.
Smaller sledgehammer = 3.0 kg X 1.5 m/s = 4.5 kg•m/s
Larger sledgehammer = 4.0 kg X 0.9 m/s = 3.6 kg•m/s
- Newton’s Third Law
Forces
Calculating Momentum
Practice Problem
A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has the greater momentum?
Golf ball: 0.045 kg X 16 m/s = 0.72 kg•m/s
Baseball: 0.14 kg X 7 m/s = 0.98 kg•m/s
The baseball has greater momentum.
- Newton’s Third Law
Forces -
Conservation of Momentum
In the absence of friction, momentum is conserved when two train cars collide.
- Newton’s Third Law
Forces - Rockets and Satellites
What Is a Satellite?
A projectile follows a curved path because the horizontal and vertical motions combine.
Forces - Rockets and Satellites
What Is a Satellite?
The faster a projectile is thrown, the father it travels before it hits the ground. A projectile with enough velocity moves in a circular orbit.
Forces - Rockets and Satellites
What Is a Satellite?
Depending on their uses, artificial satellites orbit at different heights.
Forces
Graphic Organizer
Friction between an unmoving book and desk
Type of Friction
Static
Occurs When Example
Sliding
Rolling
Fluid
An object is not moving
Two solid surfaces slide over each other
Rubber pads on a bicycle’s brakes
An object rolls across a surface
Ball bearings in skateboard wheels
A solid object moves through a fluid Air resistance