Newton s Laws of Motion 1 of 28 Boardworks Ltd 2016
Newton s Laws of Motion 2 of 28 Boardworks Ltd 2016
Introducing balanced forces 3 of 28 Boardworks Ltd 2016
What is Newton s first law? 4 of 28 Boardworks Ltd 2016 If the resultant force acting on an object is zero, all the forces are said to be balanced. This forms the basis of Newton s first law of motion, which states: If the forces on an object are balanced, the object will continue to do what it is already doing: if the object is stationary, it will remain stationary if the object is moving, it will continue to move at the same velocity (at the same speed and in the same direction). The tendency of an object to continue in its state of rest or uniform motion is called inertia.
Balanced and unbalanced forces 5 of 28 Boardworks Ltd 2016 Newton s first law tells us that the forces acting on an object that is travelling at a constant velocity are balanced. For example, when a car travels at a constant speed in a straight line, the resistive forces acting on the car balance the driving force. Newton s first law also tells us that an object that is changing speed or direction must have unbalanced forces acting on it. If the forces acting on the object are unbalanced, there is a resultant force acting on the object.
Examples of the first law? 6 of 28 Boardworks Ltd 2016
The effect of resultant forces 7 of 28 Boardworks Ltd 2016
Newton s Laws of Motion 8 of 28 Boardworks Ltd 2016
Introducing unbalanced forces 9 of 28 Boardworks Ltd 2016
What is Newton s second law? 10 of 28 Boardworks Ltd 2016 If the resultant force acting on an object is not zero, the forces on the object are said to be unbalanced. The object will therefore change velocity. This may be a change in speed, direction or both. This forms the basis of Newton s second law of motion, which states: The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.
How is acceleration calculated from force? 11 of 28 Boardworks Ltd 2016 Newton s second law of motion can be written as an equation: force = mass acceleration Force is the resultant force of all the forces acting on an object and is measured in newtons (N). Mass is measured in kilograms (kg). Acceleration is measured in metres per second per second (m/s 2 ).
How do we use the equation? 12 of 28 Boardworks Ltd 2016 A car has a mass of 1,000kg. What force must the car s engine supply to cause an acceleration of 2m/s 2? force = mass acceleration = 1,000 2 = 2,000N
Using a formula triangle 13 of 28 Boardworks Ltd 2016 A formula triangle helps you to rearrange a formula. The formula triangle for force (F), mass (m) and acceleration (a) is shown below. Cover the quantity that you are trying to work out to find the rearranged formula needed for the calculation. So to find acceleration (a), cover up a which gives the formula a = F m
14 of 28 Boardworks Ltd 2016 How do we find acceleration? A lorry has a mass of 12,000kg. What acceleration is caused by a force of 10,000N? force = mass acceleration acceleration = = force mass 10,000 12,000 = 0.83m/s 2
Inertial mass 15 of 28 Boardworks Ltd 2016 Inertia is the tendency of an object to continue in its state of rest or uniform motion. Newton s second law tells us that an object with a higher mass will require a larger force in order to change its speed or direction. This means that the mass of an object is a measure of its inertia. The inertial mass of an object tells you how difficult it is to change the velocity of the object. It is defined as the ratio of force over acceleration.
Investigating force and acceleration 16 of 28 Boardworks Ltd 2016
Investigating mass and acceleration 17 of 28 Boardworks Ltd 2016
F = ma calculations 18 of 28 Boardworks Ltd 2016
Newton s Laws of Motion 19 of 28 Boardworks Ltd 2016
What is Newton s third law? 20 of 28 Boardworks Ltd 2016 Forces arise from interactions between two objects. A force cannot exist on its own a force always causes a reaction in the form of a second force. This forms the basis of Newton s third law of motion, which states: If object A exerts a force on object B, then object B exerts an equal but opposite force on object A. These pairs of forces that act between two objects are sometimes called action reaction pairs or interaction pairs.
Action reaction pairs 21 of 28 Boardworks Ltd 2016
What forces support objects? 22 of 28 Boardworks Ltd 2016 What forces are acting between Mel s computer and the table it is resting on? The computer pushes down on the table because it is attracted by the Earth s gravity. contact force The table exerts an equal and opposite force pushing upwards on the computer. This is called the reaction of the surface. reaction force
Reaction of the surface 23 of 28 Boardworks Ltd 2016 If the downward force exerted by a stationary object increases (for example, if it gets heavier), the reaction of the surface will also increase to match it. This remains true up to a certain limit, when the downward force overcomes the reaction of the surface. At this point, the object will move downwards through the surface.
Reaction forces and thrust 24 of 28 Boardworks Ltd 2016
Newton s Laws of Motion 25 of 28 Boardworks Ltd 2016
Glossary 26 of 28 Boardworks Ltd 2016
Examples of Newton s laws 27 of 28 Boardworks Ltd 2016 How many pairs of balanced, unbalanced and action reaction forces can you spot?
Multiple-choice quiz 28 of 28 Boardworks Ltd 2016