Summary
Stretching forces involve applying more than one force to change the shape of an object. Deformation means changing shape. Elastic Deformation — The object returns to its original shape when the load is removed. Example: Elastic band. Plastic Deformation — The object does not return to its original shape when the load is removed. Example: A spring when pulled too far. Hooke’s Law — Within the elastic limit, the extension of an object is directly proportional to the force causing the extension. Example: Stretching a spring with weights.
Exam Tips
Key Definitions to Remember
- Deformation: Changing shape of an object
- Elastic Deformation: Object returns to original shape after load is removed
- Plastic Deformation: Object does not return to original shape after load is removed
- Hooke’s Law: Extension is proportional to force within elastic limit
Common Confusions
- Confusing elastic and plastic deformation
- Misunderstanding the limit of proportionality
Typical Exam Questions
- What is Hooke’s Law? Hooke’s Law states that extension is directly proportional to force within the elastic limit.
- What happens when a spring is stretched beyond its elastic limit? It undergoes plastic deformation and does not return to its original shape.
- How do you calculate the load on a spring? Use the formula W=mg, where W is weight, m is mass, and g is acceleration due to gravity.
What Examiners Usually Test
- Understanding of elastic and plastic deformation
- Ability to apply Hooke’s Law in calculations
- Interpretation of extension-load graphs