Physics: Forces and Motion

Speed Speed: the distance traveled by an object during a given time Average Speed = Distance Time S = D T

Example A cheetah ran 4 km in 2 minutes. What was the cheetah’s average speed? S = D * Don’t forget units! * T S = 4 km 2 min S = 2 km/min

Finding Distance and Time What if you are given the speed but have to find the distance or the time? Original formula: S = D T D = S X T T = D S

Examples If a coyote can run at 43 mph, how far can one go in 30 min? Make sure your units match up! D = S X T D = 43 mph X 0.25 hrs D = 10.75 mi

What would your answer be in minutes? Examples cont. If a black mamba can slither at 20 mph, how long would it take to go 1 mile? Make sure your units match up! T = D S T = 1 mi 20 mph T = 0.05 hr What would your answer be in minutes? 0.05 hours X 60 min = 3 min

Velocity Velocity: Speed that has a Direction A car that is moving 40 mph West A person that is walking 3 mph Northeast A ball that was thrown 2 mph “up”

Acceleration Acceleration: the rate at which velocity (speed) changes Can be changes in speed Bus moving down street Can be changes in direction Staying same speed around a curve on a bike Can be changes in both speed and direction. Roller coaster

Calculation Accleration Acceleration= change in velocity total time OR a= (vfinal-vintial) t

Force Force: a push or pull that acts on an object Causes resting objects to move Causes moving objects to accelerate Measurement: Newton (N) Representation: Arrow

Balancing Forces Balanced Force: no movement Unbalanced Force: object(s) forced to accelerate

Friction Friction: force slows down an object as the object moves past Without friction: walking on ice Static Friction: force acting on object at rest Sliding Friction: opposes direction of object in motion

Gravity Gravity: Force that acts downward toward the center of the Earth Does not require contact to act Upward force usually balances the force of gravity Falling Objects: Gravity causes objects to accelerate downward Air resistance is the balancing force

Terminal Velocity Terminal Velocity: velocity of object when air resistance equals force of gravity

Newton’s Laws of Motion Isaac Newton: Important in the study of mass, force and motion Newton’s 1st Law of Motion: the motion of an object does not change as long as the net force is zero Object won’t move unless something moves it!! Object won’t stop moving unless something stops it

Newton’s Laws of Motion Newton’s 1st Law of Motion a.k.a Law of Inertia: Soccer ball won’t move until someone kicks it Soccer ball will keep moving after kicked until something stops it

Newton’s Laws of Motion Newton’s 2nd Law of Motion Force of an object is equal to the mass times the acceleration of an object F =ma What is the force of an object with an acceleration of 12 m/hr2 and a mass 1000 kg?

Newton’s Laws of Motion Newton’s 2nd Law of Motion Also applies with a force that acts in the opposite direction In a collision, the seatbelt applies a force that opposes a person’s forward motion

Newton’s Laws of Motion Newton’s 3rd Law of Motion: Whenever an object exerts a force on a second object, the second object exerts an equal and opposite force on the first object For every action there is an equal and opposite reaction Called ACTION AND REACTION forces

Newton’s Laws of Motion Action Reaction Forces Hand pushing on wall: action force Wall pushing on hand: reaction force Doesn’t mean an object won’t move If the action reaction forces are on the same object…no movement If the action reaction forces are on different objects….movement can occur

Momentum Momentum: Inertia in motion. Momentum is determined by multiplying the mass and velocity of an object. The larger the mass, the more momentum The larger the velocity, the more momentum Momentum= Mass x Velocity p=mv

Momentum Two cars collide. Car A has a mass of 5000 kg and was traveling 35 km/hr west. Car B has a mass of 1000 kg and was traveling 35 km/hr east. After the collision, what direction did both cars travel

Collisions - Elastic Elastic – a collision in which the total kinetic energy of the objects before and after collision is equal Two objects collide and bounce off one another.

Elastic Collisions

Collisions - Inelastic Inelastic - a collision in which kinetic energy is not conserved. (the kinetic energy before and after the collision is NOT equal) Two objects collide and stick together and move with the same velocity

Inelastic Collisions

What kind of collision is this?

What kind of collision is this?

What kind of collision is this?

What kind of collision is this?

What kind of collision is this?

Sources http://www.kidsbiology.com/library/image.php?src=/images/repository/Dendroaspispolyepis1163275579.jpg&width=300&height=400 http://images.google.com/imgres?imgurl=http://www.bergoiata.org/fe/felins/High%2520Velocity,%2520Cheetah.jpg&imgrefurl=http://blue1.emerson.u98.k12.me.us/chaplinzoo/cheetah&h=768&w=1024&sz=126&hl=en&start=1&um=1&tbnid=IheYvOcJaYI1IM:&tbnh=113&tbnw=150&prev=/images%3Fq%3Dcheetah%26svnum%3D10%26um%3D1%26hl%3Den%26sa%3DN http://images.jupiterimages.com/common/detail/11/14/22411411.jpg http://reinvent.k12.wv.us/lt/ltactivity.nsf/forPrinting/79C04FD22576E42D8525697000694035?OpenDocument http://www.glenbrook.k12.il.us/gbssci/phys/Class/BBoard.html