motion, acceleration, and forces physical science 2012-2013
TRANSCRIPT
Motion, Acceleration, and Forces
Physical Science2012-2013
MotionSection 3-1
• Motion is a change in position of an object
Distance vs. Displacement
Distance
• The total length of the path an object follows:
Displacement
• The distance and direction of an objects final position from its initial position
• Displacement includes both a length/size and direction and is called a vector
What is the actual displacement?
Speed
• The distance an object travels per unit time.• We use metric (SI) units and it is meters per
second (m/s)• Usually the speed of an object changes as it
moves from one place to another
Instantaneous Speed
• The speed of an object at a single point in time
• Speedometer
Average Speed
• The total distance traveled divided by the total travel time
___ V = d/t
____ V = average speed d=distance t=time
Practice Problems
• What is the average speed of a car that travels a distance of 750m in 25s ?
• What is the average speed of a motorcycle that travels a distance of 300m in 10s ?
• What is the average speed of an airplane traveling a distance of 1000m in 10s ?
Velocity
• The speed of an object and the direction of the motion
• Objects have different velocities if they are moving in different directions or a different speeds
Graphing VelocityTime vs. Distance Graph
AccelerationSection 3-2
• Acceleration is the change in velocity divided by the time it takes that change to occur
Changing Direction
• A change in velocity can be either a change in how fast something is moving or a change in the direction of the movement
Calculating Acceleration
• When an object moves from one place to another, it might speed up, slow down, and change directions many times.
• Each change in velocity causes the acceleration of the object to change
Acceleration Equation
Calculation Positive Acceleration
• An airplane starts at rest and moves down the runway in a single direction. After accelerating for 20s it reaches a speed of 80m/s. What is the acceleration?
Calculating Negative Acceleration
• A car is moving in a straight line at a constant sped of 3m/s and comes to a complete stop in 2s. What is the acceleration?
Motion and ForcesSection 3-3
What is Force?
• Force is a push or pull that one object exerts on another
• Force can cause the motion of a object to change.
Baseball, Tennis, and Billiards
Balanced Forces
• Force does not always change velocity, two or more equal forces acting on an object in opposite directions can cancel each other out. The net force is zero.
Unbalanced Forces
• Unequal forces applied in opposite directions lead to a net force in the direction of the larger force and movement in that direction
Friction
• The force that opposes the sliding motion of two surfaces that are in contact
What Causes Friction?
• Frictional force depends on the materials that the surfaces are made of and the roughness of the two surfaces
• All surfaces have bumps and dips in them that can cause contact and thereby friction (microwelds)
Frictional Force
• FF increases when the force pushing the surfaces together increases.
Static Friction
• The frictional force that prevents two surfaces in contact from sliding past each other. Once the applied force is greater, the object will move.
Rolling Friction
• Rolling friction is usually much less that static friction, that is why we use wheels!
Air Resistance
• This force opposes the motion of objects that move through the air.
• Air resistance acts in the opposite direction of the objects movement
• The greater the surface area of the object the greater the power of air resistance on that object
More surface area means a slower fall
Terminal Velocity
• As an object falls it accelerates due to gravity, however air resistance eventually steps in to slow the object to a speed that no longer increases…that equaled out speed is called terminal velocity!