Locomotion. Locomotion. Ways that animals transport themselves from one place to another. Animals have appendages that are well suited for locomotion in their environment Humans – legs Fish – fins and bodies Birds - wings.
Locomotion Ways that animals transport themselves from one place to another
Animals have appendages that are well suited for locomotion in their environment Humans – legs Fish – fins and bodies Birds - wings
Animal bodies are suited for controlling forces involved in locomotion
Locomotion and Laws of Motion Locomotion is controlled by Newton’s Laws of Motion, particularly forces
Inertia Tendency of an object to resist any change in motion A moving object stays moving An object at rest stays at rest
Mass and Inertia More mass an object has, the more inertia it has More mass, harder to change the motion
Newton’s First Law Law of inertia An object moving at a constant velocity keeps moving at that velocity unless a net force acts on it.
Newton’s First Law An object at rest, stays at rest unless a net force acts on it.
Speed (rate) Rate of change in position How fast or how slow
Velocity Speed with a direction Vector Constant velocity is constant speed in one direction
Newton’s 1st Law of Motion Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.
1st Law Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!
Newton’s 1st Law and You Don’t let this be you. Wear seat belts. Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 km/hour.
First law and Locomotion Locomotion on Land – ground applies a force on the animal Water – water applies a force on the fish Air – air molecules apply a force on the bird
Newton’s 2nd Law of Motion Law of acceleration The net force on an object is equal to the product of its mass and acceleration, or F=ma.
Force A force is a push or pull one body exerts on another
Acceleration Rate of change in velocity Change in speed over time Change in direction
Acceleration Units for acceleration – m/sec2 Acceleration refers to increasing speed, decreasing speed (deceleration, negative acceleration), or changing direction
Calculating Acceleration F = mass x accelaccel = Force mass Acceleration = Final speed – Initial speed Time A plane travels from 0 m/s to 24 m/s in 3 sec. What is its acceleration? Acceleration = 8m/s2
Second law and Locomotion When an animal accelerates – speeds up, slows down, or changes direction – the acceleration is directly proportional to the force applied and inversely proportional to the animal’s mass
Newton’s 3rd Law of Motion For every action, there is an equal and opposite reaction.
3rd Law According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.
3rd Law There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces.
Action Reaction Forces don’t cancel The forces exerted by two objects on each other are often called an action-reaction force pair. Either force can be considered the action force or the reaction force. Action and reaction force pairs don’t cancel because they act on different objects.
Newton’s 3rd Law in Nature Consider the propulsion of a fish through the water. A fish uses its fins and body to push water backwards. In turn, the water reacts by pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards).
Flying gracefully through the air, birds depend on Newton’s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.
Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downward and/or backward) is opposite the direction of the force on the bird (upward and/or forward). Action-reaction force pairs make it possible for birds to fly.
Other examples of Newton’s Third Law The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction).
3rd Law and Locomotion Animals can’t apply external forces to themselves. They generate internal forces through the contraction of the their muscles and apply external forces to their environment The Earth, water, or air exerts and equal and opposite force on the animal, propelling them forward
3rd Law and Locomotion Force pairs don’t cancel each other out because they act on different objects One force acts on the Earth, water, or air Other force acts on the animal (on the foot, fin or body, or wing)
Locomotion on the ground Many land animals have legs and some form of feet to exert force on the ground One force acts on the Earth, water, or air Other force acts on the animal
Relationship between leg length and stride length Stride length – distance between foot strikes of the same leg Leg length – distance between top of femur (upper leg bone) and the ground Galloping horse and cheetah, stride length examples
Relationship between leg length and stride length If the leg is like a pendulum: L1 is length of shorter leg L2 is length of longer leg d1 is stride length of shorter leg d2 is stride length of shorter leg Studies show that longer legs usually have longer stride lengths In Investigation 2, some bear crawl results do not follow this pattern Possible error sources – counting strides, measuring leg length, maintaining leg length
Locomotion in water Forces that affect movement in water include drag force, thrust force, and lift force Drag force – force of fluid pushing against an object Drag force is opposite to direction of motion of the object Lift force is perpendicular to motion of the object Thrust force is in the same direction as motion of the object
Locomotion in water Drag force and thrust force are related to surface area Drag force is also related to the shape and smoothness of the object (coefficient of drag), fluid density, and relative velocity squared In Investigation 3, only the influence of surface area on drag force is considered
Locomotion in water Fish have a relatively small front surface area to minimize drag force Fins, side of the body, and webbed feet all have large surface areas to increase thrust force (propulsive force) Thrust force acts in the direction of motion Aquatic animals push water backwards and the water pushes the animal forwards
Locomotion in air Drag force in air also occurs directly opposite to the relative motion of an object. The drag force on a falling object acts upward The drag force on a object moving parallel to the ground, will be parallel to the ground in an opposite direction to the movement Lift force is perpendicular to the motion, whichever direction motion should be
Locomotion in air In Investigation 4, drag force of falling objects is investigated Mass is kept constant so the force of gravity is also constant, surface area changes Surface area and drag force in air:
http://www.neok12.com/Types-of-Forces.htm Website for review of forces and quizzes