Motion Unit Chapter 10

Measuring Motion Motion is the change in an object’s position. Reference point is a stationary object that is used to compare an object’s motion. Displacement is the change in position of an object. Straight line. Must be in a particular direction.

Speed Speed is how fast an object moves. v = d ÷ t Common unit for measuring speed is m/s distance time Speed is illustrated in a distance-time graph. Time on the x-axis Distance on the y-axis Horizontal line indicates that the object is not moving.

Types of Speed Constant speed is speed that does not change. Average speed is the distance traveled by an object divided by the time the object takes to travel that distance. Instantaneous speed is speed measured in an infinitely small time interval.

Velocity Velocity is speed and direction. Common unit for velocity is m/s north distance time direction

Acceleration Chapter 10, section 2.

Acceleration is the rate at which velocity changes over time Speed changes Increasing Decreasing Direction changes If you travel in a circle at a constant speed, you’re accelerating because you are constantly changing directions.

Centripetal Acceleration Centripetal acceleration is the acceleration that occurs in uniform circular motion

Calculating Acceleration acceleration = vfinal-vinitial/time or a = v/t Small acceleration, velocity is increasing very gradually Large acceleration, velocity is increasing more rapidly Positive acceleration always means a the object’s velocity is always increasing

Negative Acceleration Negative acceleration means the object’s velocity is decreasing

Graphing acceleration Plot the time on the x-axis Plot the velocity on the y-axis A straight line indicates positive acceleration Positive slope represents speeding up Negative slope represents slowing down Slope is zero if the acceleration is zero

Balanced and unbalanced forces A force is an action exerted on a body in order to change the body’s state of rest or motion A force has a magnitude and direction The net force is the combination of all of the forces acting on the object The object accelerates in the direction of the net force. The object will not accelerate if the net force is zero.

Balanced and unbalanced forces Balance forces do not cause an object at rest to start moving Net forces are zero Unbalanced forces cause the object to move in the direction of the greater force Net forces are greater than zero

Force of friction Friction is a force that opposes motion between two surfaces that are in contact The rougher the surface, the greater the friction Static friction is the force that resists the initiation of sliding motion between two surfaces that are in contact and at rest

Force of friction Kinetic friction is the force that opposes the movement of two surfaces that are in contact and are sliding over each other Sliding friction occurs when objects pass each other Rolling friction occurs when a round object rolls over a flat surface

Force of friction Static friction is usually greater than kinetic friction Fluid friction is the friction between air and the surface of the moving object Air is displaced as an object moves Air resistance increases as the speed of the object increases Designing a shape of a car to displace less air is called streamlining

Friction and motion Friction is necessary, but sometimes harmful Friction can be reduced by lubricants Friction can be increased by making surfaces rougher Hydroplaning occurs when water is trapped between the tires of a car and the road.

Review Questions What do you call a stationary object that is used for a comparison to detect motion? (reference point or reference frame) What do you call the distance between the starting point to the final destination? (displacement) What describes how fast an object moves? (speed) What is the type of speed when equal distances are covered in equal time? (constant speed) What is graphed on the x-axis of a speed graph? (time) What is graphed on the y-axis of a speed graph? (distance)

Review Questions What do you call the total distance the object traveled divided by the total time it took for the object to move that distance? (average speed) What is speed measured in infinitely small time intervals? (instantaneous speed) What do you call speed with direction? (velocity) What is the formula for calculating speed? (v = d/t) What is the formula for calculating acceleration? (a = (vf –vi)/t What do we call the rate in change of velocity? (acceleration)

Review Questions What do we graph on the y-axis of an acceleration graph? (speed) What type of forces causes change in motion of an object? (unbalanced forces) What type of forces causes no change in the motion of an object? (balanced forces) What is a force? (a push or pull) What do we call the force that resist a surface moving over another surface? (friction) What is the type of friction where everything is stationary? (static friction)

Review Questions What type of friction involve moving objects? (kinetic friction) What are the two types of kinetic friction? (sliding friction & rolling friction) What type of friction is air resistance? (fluid friction) What reduces friction? (lubricants)

Review Questions

Review Questions

Review Questions