1. Physics Unit Four Forces that Affect Motion

2. Force A push or a pull. Measured in newtons with a spring scale. 1 newton (N) = 1 kg m/s 2 An apple weighs about 1 newton. Calculate your weight in newtons: Weight in pounds = _____ 2.2 lbs/kg Mass in kg = _____ x 9.8m/s 2 = Weight in newtons _____ N

3. Forces that affect motion F a Applied Force –a force exerted on an object by other objects in it’s environment. F f Frictional Force – a force that opposes motion between the object and the surface it rests upon F g Gravitational Force – the force of attraction between two objects with mass (ex. Between an object and the Earth, for example) F n Normal Force – the supportive force of the surface an object rests upon. It is equal to the force of gravity acting on the object. Normal means “perpendicular”

4. If forces are balanced… No Motion No net (unbalance) forces. FgFg FnFn FfFf FfFf FgFg FnFn

5. If forces are balanced… No Motion No net (unbalance) forces. FgFg FnFn FgFg FnFn 50N, up 50N, down

6. If forces are unbalanced… Motion Net (unbalanced) force. FgFg FnFn Direction of motion FnFn FgFg

7. Force Equations Acceleration –According to Newton’s 2nd Law of motion, the acceleration of an object is equal to the net force acting on it divided by the object’s mass –Formula: A = F / m –Therefore, doubling the mass of an object cuts its acceleration in half –The unit for acceleration is m/s 2

8. Force –Force on an object is equal to its mass and acceleration –Formula: F= m(a) Force Equations

9. Weight –Weight is the force of gravity acting on an object –Formula: W= m(g) –The unit for weight is also newtons because it is a force Force Equations

10. Momentum –Momentum is the product of an object’s mass and its velocity –An object has a large momentum if the product of its mass and velocity is large. –Formula: Momentum ( P)= m(v) –The unit for momentum is kg*m/s Force Equations