Forces and Newton’s Laws Chapter 3

Force Force is the cause of acceleration, or change in an object’s motion. (Push or a Pull) Examples -Throwing or catching a ball, pushing a cart, pulling a cart Formula Force = Mass (kg) x Acceleration (m/s 2 ) Unit for Force is a Newton (N).

Friction – Type of Force Friction is the force between two objects touching that opposes the forward motion of the object. What type of surface creates more or less Friction?

Air Resistance/Friction – Type of Force Air Resistance- is a type of friction between air particles and an object. The amount of air resistance depends on size, shape and speed. How has the design of old vs new vehicles changed and why?

Gravity- A Type of Force Gravity- an attractive force between two objects that depends on the masses of the objects and the distance between them. Gravity depends on Mass and Distance

Weight - Type of force Weight is the gravitational force exerted on an object. F = m x a to solve for your downward force Convert your mass example lbs into kg by dividing by 2.2kg so 150/2.2 = 68.18kg Use the acceleration due to gravity 9.8m/s 2 for acceleration F = 68.18kg x 9.8 m/s 2 = N As you can see weight is different than mass because weight takes into account that you have gravity (9.8m/s 2 ) pulling you down. Solve for your Weight/downward Force

Net Force – Weight, Gravity and Friction acting on object’s motion Net force - the combination of all forces acting on an object. (weight, friction, gravity) These forces will determine whether the velocity of the object will change.(or whether the object will move) Label the forces not pictured

Unbalanced Force Unbalance fore- forces acting on an object that combine to produce a net force that is not zero. (a force that causes an object to move) Pusher #1 = 20N and Puller #1 = 10N Both force is same direction so add both together. 20N + 10N = 30N going to the right

Examples of Unbalanced Forces 50N & 40N = 10N Opposite direction - subtract Same direction - add

Balanced Force 30N pushing to left and 30N pushing to right, forces are in opposite direction so subtract 30N - 30N = 0N (no motion) Balanced Force - forces on an object that combine to produce a net force of zero Balanced force equals no movement

Examples of Balanced Forces 20 N - 20 N =0 N5N - 5 =0 N NO MOVEMENT = BALANCED

Newton’s Laws of Motion Chapter 3 Section 2

Newton’s Laws of Motion 1 st Law or Law of Inertia An objects motion remains unchanged unless an outside force acts upon it. An object in motion remains in motion or an object at rest remains at rest unless acted upon by an outside force. Watch 1st law

1 st Law, Inertia Examples

Newton’s Laws of Motion 2 nd Law or F=mxa An objects motion is changed by a Force (N) which is equal to Mass (kg) x Acceleration (m/s 2 ) So Force = Mass x Acceleration or F = m x a Triangle If an object is falling due to Gravity then use a=9.8m/s 2 (watch 2 nd law )

2 nd Law, F=m x a Examples F = 1,000kg x.05 m/s 2 = 50N

#1 F = m x a What is the net force necessary for a 1600 kg automobile to accelerate forward at 2.0m/s 2 ? DataFormulaWorkAns F=F=m x a m= a=

#2 F=mxa 2. A baseball accelerates downward at 9.8m/s 2, if the ball has a mass of.14kg how much force was applied to the ball? DataFormula WorkAns F= m= a=

Newton’s Laws of Motion 3 rd Law of Motion, Action Reaction Law An objects motion is changed by a force which causes an action reaction For every action there is an equal and opposite reaction. (watch 3rd)

Newton’s 3 rd Law, Action Reaction Law Examples