#### Transcript What Is a Force?

12.1 Forces Bellringer 2/22 1. What do you think is a force? 1. Name some forces you can think of off the top of your head. 1. How do you think we measure forces? 12.1 Forces What Is a Force? A force is a push or a pull that acts on an object. Forces can cause resting objects to move, or it can accelerate a moving object by changing the object’s speed or direction. 12.1 Forces What Is a Force? Measuring Force You may have measured forces using a spring scale. 12.1 Forces What Is a Force? Units of Force One newton (N) is the force that causes a 1kilogram mass to accelerate at a rate of 1 meter per second each second (1 m/s2). 1 N = 1 kg•m/s2 12.1 Forces What Is a Force? Representing Force Arrows can represent a force. The lengths of the arrows show relative amounts of force. 12.1 Forces Combining Forces When the forces on an object are balanced, the net force is zero, and there is no change in the object’s motion. When an unbalanced force acts on an object, the object accelerates. 12.1 Forces Combining Forces The net force is the overall force acting on an object after all the forces are combined. • Forces in the same direction add together. • Forces in opposite directions subtract from one another. 12.1 Forces Combining Forces Forces can add together or subtract from one another. Adding forces 12.1 Forces Combining Forces Forces can add together or subtract from one another. Adding forces Subtracting forces 12.1 Forces Combining Forces Forces can add together or subtract from one another. Adding forces Subtracting forces Equal and opposite forces 12.1 Forces Combining Forces The two groups pull with equal forces in opposite directions. The forces combine to make a net force of zero. 12.1 Forces Bellringer 2/23 1. What is a force? 1. What happens when a balanced force acts upon an object? 1. What happens when an unbalanced force acts upon an object? 12.1 Forces Calculating Forces • To calculate any force, we use the formula: Force= mass x acceleration OR F=ma 12.1 Forces Important units • Force: 1 N = 1 kg•m/s2 • Mass: – Base unit is grams g • Acceleration: m/s2 – Remember! 1000g=1kg 12.1 Forces Guided Practice Label the following units as force, mass, or acceleration: • Grams • m/s2 x kg • m/s2 • kg x m/s2 • N • kg: 12.1 Forces Guided Practice A man hits a golf ball (0.2 kg) which accelerates at a rate of 20 m/s2. What amount of force acted on the ball? 12.1 Forces Guided Practice You push a friend sitting on a swing. She has a mass of 50 kg and accelerates at a rate of 4 m/s2. Find the force you exerted. 12.1 Forces Guided Practice The wind pushes a paper cup along the sand at a beach. The cup has a mass of 0.025 kg and accelerates at a rate of 5 m/s2. How much force is the wind exerting on the cup? 12.1 Forces FUN STUFF • Weekly Writing Due Friday 2/26 • Homework Due Friday 2/26 12.1 Forces Friction Friction is a force that opposes the motion of objects that touch as they move past each other. 12.1 Forces Gravity In what direction does Earth’s gravity act? Earth’s gravity acts downward toward the center of Earth. 12.1 Forces Gravity How do gravity and air resistance affect a falling object? Gravity causes objects to accelerate downward, whereas air resistance acts in the direction opposite to the motion and reduces acceleration. 12.1 Forces Gravity Gravity is a force that acts between any two masses. • Gravity is an attractive force. • Gravity can act over large distances. 12.1 Forces Gravity Earth exerts an attractive, downward force on this boulder. The supporting rock exerts an upward force on the boulder. The forces are balanced. 12.1 Forces Gravity Falling Objects • Both gravity and air resistance affect the motion of a falling object. • As objects fall to the ground, they accelerate and gain speed. • Terminal velocity is the constant velocity of a falling object when the force of air resistance equals the force of gravity. 12.1 Forces Gravity This flying squirrel takes advantage of air resistance to slow its fall and increase the distance covered in the jump.