Forces Change Motion

50 N 50 N 25 N 17 N

Force Force Is a push or pull Is used to change the motion and direction of objects Is a vector, which means that force has both size and direction. Example: You use force when you pick up your backpack. Force

Force Contact force is when an object pushes or pulls on another object by touching. Gravity is the force of attraction between 2 masses. Friction is a force that resists motion. Types of forces

Forces Net force – is the overall force acting on an object, when all forces are combined. If the net force on an object are zero, they are balanced. Balanced forces have the same effect as NO force at all. Only unbalanced forces can change the motion of an object. Balanced and Unbalanced Forces

Force Force is measured in newtons.(N) Force is measured with a spring scale. When calculating net force: If the forces are going the same direction you add the newtons. If the forces are going in the opposite direction you subtract the newtons. Calculating Net Force

Newton’s 1st Law of Motion Is the resistance of an object to a change in the speed or direction of its motion. Examples of the effects of inertia are Inertia causes a passenger in a car to move forward even though the car stops. Inertia is the reason that it is harder to start pushing a wheelbarrow full of brick than to start pushing an empty wheelbarrow. Why is this true? Inertia

Inertia Another example of inertia explains why it is harder to stop a loaded truck going 55mph than to stop a car going 55mph. Why is this true?

Mass Is a measure of how much matter an object is made of. If a heavy object (more mass) is in motion, more force must be applied to get the object to move faster. If the same force is applied to 2 objects, the object with the smaller mass changes speed more quickly.

Mass cont. It is more difficult to change direction of a heavy moving object, than one with lighter mass. In order to slow down or stop an object with more mass, the force on that object must be greater than the object with less mass.

Newton’s 2nd Law of motion This law states that the acceleration of an object increases with increased force and decreases with increased mass. The law also states that the direction in which the object accelerates is the same as the direction of the force. Acceleration – is the rate at which velocity changes over time.

Force = mass · acceleration or F=ma Newton’s 2nd Law Force = mass · acceleration or F=ma If the same force acts on 2 objects , the object with less mass will have the greater acceleration. Ex: pushing a soccer ball and a bowling ball. Which would have the greater acceleration? the soccer ball

Newton’s 3rd Law

Newton’ 3rd Law This law states that for every action there is an equal and opposite reaction. The force that is exerted on an object and the force that the objects exerts back are known together as action/reaction forces. Action/reaction forces are not the same as balanced. Balanced forces act on only one object. Action/Reaction forces act on different objects.

Friction resists motion between surfaces in contact with each other. greater the pressure, greater the friction. rougher the surface the greater the friction.

Gravity Is a force that always attracts or pulls objects to toward each other without contact. Gravitational attraction depends on the mass of the 2 objects and the distance they are apart. Objects on Earth are pulled toward the center of the Earth. The force of gravity can cause changes in the speed of objects.

Gravity The pull of the Earth’s gravity keeps the moon in orbit.