2 What is Force? A force is a push or pull. The wind pushes against a sail or a magnet pulls iron toward itA force gives energy to an object, sometimes causing it to start moving, stop moving or change direction.If force is increased then movement increasesYou exert a force on an object & the object exerts a force on you.
3 Combining Forces Force involves direction Same Direction = when 2 forces act in the same direction they are added togetherOpposite Direction = when 2 forces act in the opposite direction they are subtractedTotal Force on an object is in one direction,the force is called UnbalancedForces that are in opposite directionand are equal in size are Balanced
5 Friction: A Force Opposing Motion Friction is a force that exists between 2 objects that are touching.It is a force that acts in the opposite direction of a moving object.Friction will cause a moving object to slow down and finally stop.
6 Friction depends on:How hard the surfaces of the touching objects are forced togetherThe heavier the objects, the more friction there will be & the harder it is to move them.The materials that the surfaces of the objects are made ofYou must exert a force that is larger than the force of friction in order to move an object.
7 Types of FrictionSliding Friction – when solid objects slide over each otherRolling Friction – produced by objects such as wheels & ball bearingsWhich has less friction? Why?Fluid Friction – force exerted by a fluid such as water, oil, airAir Resistance slows down falling objects
8 Additional Facts ….Lubricants = “slippery” substances that help reduce frictionChange from sliding to fluid frictionGrease, oil, waxWhy is Friction a Good Thing?
9 Sir Isaac Newton Born: 4 Jan 1643 in Lincolnshire, England Died: 31 March 1727 in London, EnglandNewton’s Laws describe all states of motion – at rest, constant motion & accelerated motion
10 Newton’s Laws of Motion First Law = states that an object at rest will remain at rest or an object in motion will remain in motion until acted upon by an unbalanced forceInertia – matter tends to resist any change in motion; the more mass an object has the more inertia it has
11 Newton’s Second Law Force = Mass X Acceleration (F=M*A) The greater the force, the more the accelerationThe more mass (thus more inertia) an object has the greater the force required for acceleration of the objectNewton – unit of measurement for ForceThe force required to accelerate 1 kg of mass 1 m/s/s
12 Newton’s Third LawStates that for every action, there is an equal and opposite reactionWhat’s going to happen to the car? In what direction will it go?
13 GRAVITYIn the 1500’s, the Italian scientist Galileo dropped 2 cannonballs of different masses from the Leaning Tower of Pisa.Both cannonballs landed at the same time.WHY?
14 Falling Objects … Galileo’s discovery was important to Newton All falling objects accelerate at the same rateThe acceleration of a falling object is due tothe force of gravity between the object & theEarth.Acceleration due to gravity (g) near the Earth’ssurface is 9.8 m/s/s
15 Newton’s Law of Universal Gravitation States that all objects in the universe attract each other by the force of gravityThe size of the force depends on:The masses of the 2 objectsThe distance between the objectsForce of gravity increases as mass of the object increasesGravitational force decreases as distance between objects increases
16 Weight and MassWeight is a measure of the force of gravity on an object (measured in Newtons)Weight = Mass X Acceleration due to GravityWt = M * gGravity = 9.8 m/s/s or 9.8 N