Newton's Laws of Motion Flashcards

Newton's Laws of Motion

Syllabus Understandings (B.2.1)

• B.2.1.1: Linear and angular motion can be analyzed using Newton's laws of motion.

  • Newton's First Law (Law of Inertia): An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by a force. This law essentially states that objects resist changes in their state of motion. For example, a soccer ball will remain motionless until a force (like a kick) acts upon it. Similarly, an ice hockey puck will continue sliding at a constant velocity until friction or another force slows it down.

  • Newton's Second Law (Law of Acceleration): The acceleration of an object is directly proportional to the net force acting on the object, is in the same direction as the net force, and is inversely proportional to the mass of the object. Expressed as F=ma, where F is force, m is mass, and a is acceleration. This law quantifies the relationship between force, mass, and acceleration. A larger force will produce a greater acceleration, while a larger mass will result in a smaller acceleration for the same force. For instance, it takes more force to accelerate a heavier medicine ball than a lighter baseball.

  • Newton's Third Law (Law of Action-Reaction): For every action, there is an equal and opposite reaction. This means that if object A exerts a force on object B, then object B exerts an equal and opposite force on object A. When you jump, your feet exert a force on the ground (action), and the ground exerts an equal and opposite force back on your feet (reaction), propelling you into the air.

• B.2.1.2: A collision results in a change in momentum in the colliding bodies.

  • Momentum is the product of an object's mass and its velocity (p=mv). In collisions, momentum is conserved in a closed system.

  • Types of Collisions: Elastic collisions (where kinetic energy is conserved) and inelastic collisions (where kinetic energy is not conserved).

  • Impulse: The change in momentum of an object. It is equal to the force applied to the object multiplied by the time for which it is applied (Impulse=FΔt).

• B.2.1.3: The force of friction is determined by the coefficient of friction.

  • Friction is the force that opposes motion between two surfaces in contact. The force of friction (FfFf) is calculated as Ff=μNFf=μN, where μμ is the coefficient of friction and NN is the normal force.

  • Static Friction: The friction that prevents an object from starting to move.

  • Kinetic Friction: The friction that acts between moving surfaces.

  • The coefficient of friction (μμ) depends on the materials of the two surfaces in contact.

• B.2.1.4: Work results from the application of a force over a distance.

  • Work is done when a force causes a displacement of an object. It is calculated as W=Fdcosθ, where W is work, F is the magnitude of the force, d is the magnitude of the displacement, and θ is the angle between the force and displacement vectors.

  • Work is a scalar quantity and is measured in Joules (J).

  • Positive Work: When the force and displacement are in the same direction.

  • Negative Work: When the force and displacement are in opposite directions.

Introduction to Newton's Laws

• Newton's laws of motion underpin the movements of the body and sporting equipment, relating forces to motion.

• These laws provide a basis for understanding how forces affect motion, enabling accurate analysis and prediction of movement.

• Understanding these laws is crucial for analyzing sporting techniques and physical activity to improve performance, reduce injury risk, and develop new techniques.

• By applying Newton's laws, coaches and athletes can optimize movements, enhance force production, and minimize the risk of injuries.

• Key terms such as force, power, velocity, and energy have specific scientific meanings that are essential for accurate analysis of human movement.

Introduction to Kinematics

• Kinematics is the study of motion, which is defined as the change in position of a body or object.

• It involves describing motion without considering the forces that cause it.

• Motion can be:

  • Linear: Movement in a straight line (e.g., an ice hockey puck sliding on ice).

  • Linear motion involves all parts of the object moving the same distance in the same direction.

  • Curvilinear: Movement in a curve (e.g., a shot-put traveling through the air).

  • Curvilinear motion involves movement along a curved path, where the direction of motion changes continuously.

  • Angular (Rotational): Movement around an axis (e.g., a gymnast rotating around a high bar).

  • Angular motion occurs when an object rotates about an axis, with different parts of the object moving through different distances depending on their distance from the axis.

  • General: A combination of linear and angular motion.

  • General motion is the most complex type of motion, involving both translation and rotation.

• General motion is the most common type of motion in sport and exercise because at almost all synovial joints in the body, one segment rotates around another.

  • Examples include running, jumping, and throwing, where limbs undergo both linear and angular movements.

Key Terms

• Vector: A measurement that has both size and direction.

  • Examples include displacement, velocity, acceleration, and force.

• Scalar: A measurement that only has size.

  • Examples include distance, speed, mass, and time.

Measurements and Position

Vector and Scalar Measurements

• Vector: Measurement with both size and direction.

  • Vectors are typically represented by arrows, where the length of the arrow indicates the magnitude and the direction of the arrow indicates the direction of the vector.

• Scalar: Measurement with only size.

  • Scalars are fully described by their magnitude and units.

• The distinction between scalars and vectors is important in biomechanics because it affects how measurements are combined (added, subtracted, multiplied, or divided).

  • Mathematical operations with vectors require considering both magnitude and direction, whereas scalars can be treated as simple numbers.

• If the direction of two vectors is the same, their sizes can be combined. If directions differ, this must be taken into account.

  • Vectors in the same direction can be added directly, while vectors in opposite directions can be subtracted.

• Scalars can be directly added, subtracted, multiplied, and divided.

  • Scalar quantities are combined using basic arithmetic operations.

Position

• The position of an object or body is usually given by its coordinates, which measure distance from an origin (e.g., in meters).

  • The origin is a fixed reference point from which all distances are measured.

• Coordinates are often given in two dimensions (horizontal and vertical) or three dimensions (horizontal, vertical, and lateral).

  • Two-dimensional coordinates are used to describe motion in a plane, while three-dimensional coordinates are used to describe motion in space.

• Two-dimensional coordinates are often named xx and yy (horizontal and vertical), while three-dimensional coordinates are usually called xx, yy, and zz.

  • The choice of coordinate system depends on the specific application and the directions of motion being analyzed.

• Two systems exist for three-dimensional coordinates: one where xx is horizontal, yy is vertical, and zz is lateral, and another where xx is horizontal, yy is lateral, and zz is vertical.

  • These are known as right-handed coordinate systems, where the axes are mutually perpendicular.

• Angular coordinates are given by measuring angles around one or more axes.

  • Angular coordinates are typically measured in degrees or radians.

Linear Kinematics

Linear Displacement and Linear Distance

• Displacement occurs when a body or object changes its position, described by how far and in what direction the end position is from the start position.

  • It is the shortest distance between the initial and final positions of the object.

• Displacement is a vector quantity with both size and direction; it's often expressed in horizontal, vertical, and lateral components.

  • The components of displacement indicate the change in position along each coordinate axis.

• Distance is the size of linear displacement and is a scalar quantity with no direction, indicating how far an object or body moves regardless of direction.

  • Distance is the total length of the path traveled by the object.

• Linear displacement is usually given by the symbol ss. Linear distance is given by the symbol dd.

  • These symbols are commonly used in kinematic equations.

• The SI unit for displacement and distance is meters (m).

  • Other units, such as kilometers, centimeters, and millimeters, may also be used depending on the scale of the motion.

• Displacement direction can be specified in degrees (∘∘) or radians (rad) from a particular direction or along a coordinate axis.

  • The direction is often given as an angle relative to the horizontal axis.

Linear Velocity

• Velocity is the change in displacement divided by the time taken for the change to occur. It is a vector quantity with both size (how fast) and direction.

  • Velocity indicates both the speed and direction of motion.

• Linear velocity is usually given by the symbol vv. Sometimes the symbol uu is used.

  • The symbol uu is often used to denote initial velocity.

• The formula for velocity is: v={\Delta s \over \Delta t}, where v is velocity, s is displacement, t is time, and \Delta means